Physical Science Solution –2019

Group-A

1. Multiple choice question.
1.1 Which among the following gases absorb long wavelength infrared radiation emitted from the earth’s surface?
(a) N2
(b) O2
(c) CH4 (Ans)
(d) He

1.2 At STP, 2.24 ltr is occupied by
(a) 4.4 g CO2 (Ans)
(b) 0.64 g SO2
(c) 28 g CO
(d)16 g O2

1.3 How many molecules of CO2 will be produced when one mole C reacts completely with one mole O2?
(a) 6.022×10^23 (Ans)
(b) 1.806×10^24
(c) 6.022×10^22
(d) 6.022×10^24

1.4 For a solid, how many types of thermal expansion coefficients are there?
(a) 1
(b) 2
(c) 3 (Ans)
(d) 4

1.5 Which one of the following has the highest wavelength?
(a) x-ray
(b) γ-ray
(c) infrared ray (Ans)
(d) Ultraviolet ray

1.6 In case of refraction, if the angle of incidence and the angle of refraction are 45° and 30° respectively, then the angle of deviation is
(a) 75°
(b) 15° (Ans)
(c) 7.5°
(d) 37.5°

1.7 Temperature remaining unchanged if the potential difference between the two ends of a conductor is V and the current through the conductor is I, which of the following is true?
(a) V∝I (Ans)
(b) V∝I²
(c) V∝I^(-1)
(d) V∝I^(-2)

1.8 The relation among electromotive force (V), work (W) and charge (Q) is
(a) Q=WV
(b) Q=V/W
(c) Q=V/W²
(d) Q=W/V (Ans)

1.9 For the atom produced by β-particle emission from a radioactive atom
(a) mass number increases
(b) atomic number increases (Ans)
(c) mass number decreases
(d) atomic number decreases

1.10 To which group of the long periodic table do the halogen elements belong?
(a) Group 1
(b) Group 16
(c) Group 17 (Ans)
(d) Group 2

1.11 Solid state of which of the following compounds is composed of ions?
(a) sodium chloride (Ans)
(b) hydrogen chloride
(c) naphthalene
(d) glucose

1.12 Which of the following has the highest ability to conduct electricity?
(a) pure water
(b) aqueous solution of sugar
(c) liquid HCl (Ans)
(d) aqueous solution of acetic acid

1.13 In the first step of fixation of nitrogen which of the following compounds is formed as a result of lightning.
(a) NO
(b) NO2
(c) N2O5 (Ans)
(d) HNO3

1.14 Which of the following is the formula of bauxite, ore of aluminium?
(a) Al2O3
(b) Al2O3H2O
(c) Al2O32H2O (Ans)
(d) AlF3.3NaF

1.15 Which of the following is the alkyl group containing two carbon atoms?
(a) methyl
(b) ethyl (Ans)
(c) propyl
(d) isopropyl

Group-B

2. Answer the following question (alternatives are to be noted).
2.1 Write down the unit of calorific value of fuel?
Ans: The unit of the calorific value of fuel is Joule per kilogram (J/Kg).
Or, Does the temperature increase or decrease with increase in altitude in the stratosphere?
Ans: The temperature increase with increase in altitude in the stratosphere.

2.2 Which radiation, coming from the sun, is prevented by the ozone layer from falling on the earth’s surface?
Ans: UV radiation , coming from the sun, is prevented by the ozone layer from falling on the earth’s surface.

2.3 State whether the following statement is true or false.
The volume of gas molecules is taken into consideration in Avogadro’s law.
Ans: This statement is true.

2.4 The product of volume and pressure of how many grams of N2 gas is 224 litre atmospheres at STP? (N=14)
Ans: The product of volume and pressure of 280 grams of N2 gas is 224 litre atmospheres at STP.

2.5 Whether the following statement is true or false?
The constituent’s particles of a material change position during conduction of heat through it.
Ans: This statement is false.
Or, The width and the cross section of a conductor remaining unchanged, what is the relation between the thermal resistance and thermal conductivity of that conductor?
Ans: R = L/KA , Where R is thermal resistance and K is thermal conductivity.

2.6 What will be the angle of incidence when a ray of light passes through the centre of curvature of a concave mirror?
Ans: Angle of Incidence is zero when a ray of light passes through the centre of curvature of a concave mirror.

2.7 How many rectangular surfaces are there in a prism?
Ans: There are six rectangular surfaces are there in a prism.

2.8 Give an example of semiconductor.
Ans: Silicon is an example of semiconductor.

2.9 A thin wire and a thick wire of the same conducting material have the same length. Which one of them will carry more current when connected to the same potential difference?
Ans: Thick wire will carry more current when connected to the same potential difference.

2.10 Mention one misuse of nuclear fission reaction.
Ans: Bombardment is a misuse of nuclear fission reaction.

Or, Which law explains the release of huge amount of energy in nuclear fusion?
Ans: Law of conservation of mass and energy explains the release of huge amount of energy in nuclear fusion.

2.11 Match the right column with the left column:

2.12 Draw the Lewis dot structure of N2 molecule, (N=7)
Ans:

2.13 Which kind of electricity is used in electrolysis?
Ans: D.C current is used in electrolysis.
Or, Write down the cathode reaction in the electrolysis of acidulated water using platinum electrodes.
Ans: Cathode reaction: H⁺ + e → [H], 2[H] → H₂    ↑ (reduction)

2.14 In electroplating gold on brass, what is the electrolyte used?
Ans: Potassium aurocyanide is used as electrolyte in elecroplating of gold on brass.

2.15 What colour is formed in the reaction of ammonia with Nessler’s reagent?
Ans: Brown coloured solution or precipitate is formed in the reaction of ammonia with Nessler’s reagent.

2.16 Write down the formula of the precipitate formed when H2S gas is passed through an aqueous solution of silver nitrate.
Ans: Ag₂S↓ is formed when H2S gas is passed through an aqueous solution of silver nitrate.
Or, Write the name of the compound which is formed by the reaction of nitrogen with magnesium metal at a high temperature.
Ans: Magnesium Nitride is formed by the reaction of nitrogen with magnesium metal at a high temperature.

2.17 What is the value of H-C-H bond angle in methane?
Ans: 109⁰28 is the value of H-C-H bond angle in methane.
Or, Write the IUPAC name of CH3CH2COOH.
Ans: The IUPAC name of CH3CH2COOH is Propanoic acid.

2.18 What is the industrial source of CNG?
Ans: The industrial source of CNG is Methane.

Group-C

3. Answer the following questions.
3.1 What is the concept of sustainable development?
Ans: Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

3.2 1g of a gas at 7°C and 2 atmosphere pressure occupies a volume of 410 ml. determine the molar mass of the gas. (R = 0.082 litre atmosphere 〖mole〗^(-1) K^(-1))
Ans:

Or, A fixed mass of gas occupies a volume of 273cm³ at STP. At what pressure the above gas will occupy a volume of 300cm³ at 27°C?
Ans:

3.3 What is the refractive index of a medium?
Ans: Refractive index, also called index of refraction,  measure of the bending of a ray of light when passing from one medium into another.
Or, Which type of defect of vision is rectified by a convex lens?
Ans: Hypermyopia is a defect rectified by a convex lens.

3.4 Two resistance r1 and r2, when connected separately to the same potential difference, it was seen that the current flowing through r1 was 6times the current flowing through r2. Determine the ratio of r1 and r2.
Ans:

3.5 How does Kossel explain the formation of ionic bond?
Ans: The formation of ionic bond was explained by Kossel as follows: * The atoms of inert gases are stable due to octet configuration (ns2np6) in their outer shell. Hence atoms must possess eight electrons in their outer shell to get more stability. These electrons are also called as valence electrons.
or, Liquid hydrogen chloride can not conduct electricity, but molten sodium chloride can conduct electricity. Explain
Ans: Liquid hydrogen chloride does not have ions in it so it does not conduct in electricity but in molten sodium chloride ions are present and are free to move also so this can conduct electricity.

3.6 Distinguish between sodium chloride and naphthalene by two physical properties.
Ans:

3.7 Between two aqueous solution, one is ferric chloride and the other is aluminium chloride. How would you identify the ferric chloride solution using aqueous solution of ammonia? Answer with balanced chemical equation.
Ans:

3.8 Why zinc blende can be called both mineral and ore of zinc?
Ans: Because it has zinc or it is made up of zinc.
Or, Mention two ways of preventing rusting of iron.
Ans: 1. Paint it – Paint the metal with any durable acrylic paint. Do not use Water-Soluable paints, since they will only worsen the rust. Rust will form underneath this type of paint.
2. Keep moisture at Bay – Avoid contact with water or moisture. We know that the water has chemical formula which corresponds to 2 parts Hydrogen and 1-part Oxygen. Hence oxygen is responsible for oxidation of iron and therefore forms rust.

3.9 Write with balanced chemical equation what happens when methane is burnt in oxygen.
Ans: Methane is CH 4 and when burnt in oxygen (air) it produces heat and CO 2 and water.
Reaction:- CH₄ +2O₂ →CO₂ +2H₂O
Or, Mention one use of each of acetic acid and ethyl alcohol.
Ans: Use of acetic acid: acetic acid which is a dilute solution is used extensively as vinegar.
Use of Ethyl alcohol: It is used in alcoholic beverages as a solvent and in making other chemicals.

Group-D

4. Answer the following questions.
4.1 What is meant by molar volume of a gas? Mention two reasons for deviation of real gasses from the behaviour of ideal gases.
Ans: The volume occupied by one-gram molecule of any gaseous substance (elementary or compound) at a fixed temperature and pressure is known as Molar Volume.
Two reasons for the deviation of real gases from the behaviour of ideal gases:
(i) In the kinetic theory of gases, the gas molecules are considered as point particles of a very small dimension and their actual value is negligible compared to the volume of the container.
But actually, the gas molecules have a volume of their own although they are extremely small. Thus, the effective volume available to the molecules of the real gases for free movement is partly less than the volume of the container.
(ii) According to the kinetic theory of gases, the molecules of the gas do not experience intermolecular forces of attraction among them. But, at high pressure the gas molecules come closer to each other, as a result, an attractive force come into play among the molecules.
Thus, the molecules of real gas fall to exert the same pressure on the wall as exerted by the molecules of the ideal gas under ideal condition.

4.2 How many grams of Al is required to prepare 558g of Fe by the reduction of Fe2O3 With Al at high temperature? How many moles of Fe2O3 be required in the reaction? (F=55.8, Al=27, O=16)
Ans: Equation for the reaction (thermite process):
Fe2O3 + 2Al = Al2O3 + 2Fe
Molar mass:
Aluminium – 26.98 g
Iron – 55.85 g
Iron(III) oxide, Fe2O3 – (55.85 X 2) + (16 X 3) = 111.70 + 48 = 159.7 g
Aluminium oxide, Al2O3 – (26.98 x 2) + (16 x 3 ) = 53.96 + 48 = 101.96 g
(1) To find the mass of aluminium required:
As per the equation, to produce 2 moles of iron, 2 moles of aluminium is required.
So, to get 1 mole of iron ((55.85 g), 1 mole of aluminium (26.98 g) will be required.
Amount of aluminium needed to get 558 g of iron = (558 x 26.98)/55.85 = 269.36 g (answer)

(2) To find the number of moles of iron(III) oxide:
Mass of iron to be produced = 558 g = 558/55.85 = 9.99 moles
As per the equation, 1 mole of Fe2O3 is required to get 2 moles of iron.
So, number of moles of Fe2O3 required to get 9.99 moles of iron = (9.99 x 1)/2 = 4.995 = 5 moles (answer).

Anwers:
(1) Mass of aluminium required = 269.36 g
(2) Number of moles of Fe2O3 required = 5 moles
Or, By heating 32.1gram ammonium chloride with calcium hydroxide 10.2g NH3 33.3g CaCl2, and 10.8g H2O are obtained. How many grams of calcium hydroxide takes part in the reaction? How many mole of NH3, and how many litre of NH3 at STP are formed in the reaction? (N=14, H=1)
Ans:

4.3 Which quantities remain fixed in the definition of volume expansion coefficient of a gas? Name a non-metal which is a good conductor of heat.
Ans: Pressure is the quantity that remains fixed in the definition of volume expansion coefficient of a gas.
Graphite is a nonmetal which is a good conductor of heat.
Or, What is meant by ‘linear expansion coefficient of copper is 17×10^(-6)/°C’? Why does the value remain the same even in Kelvin scale?
Ans: Copper fractional expansion per degree C × 10⁶: 17
Fractional expansion for degree F × 10⁶: 9.4

4.4 What type of mirror is used by the dentists? Why a ray of light does not deviate as a result of refraction through a glass slab?
Ans: Concave Mirror is used by the dentists.
the reflection of light in glass prism is different from glass slab this is because in glass prism the incident ray of light Is not parallel to emergent ray of light when a ray of light get enters in glass prism it gets deviated two times.

4.5 When an object is placed 20cm away from a convex lens, no image is obtained on either side of the lens. What is the focal length of the lens? If the refractive index of glass with respect to air is 1.5, what is the refractive index of air with respect to glass?
Ans: As there is no image formed at either side of the lens so there is only one condition that is the object is placed at the focus of the lens.
Focal length of the lens is 20cm.
Refractive index of air with respect to glass
=refractive index of air/refractive index of glass
=1/1.5 =0.67
Or, The length of an object is 5cm. An image of length 10cm is obtained when it is placed at distance of 2cm in front of a convex lens. What is the linear magnification and image distance?
Ans: u =- 10 cm for convex mirror, the object distance is -ve.
v=?, R= 30 cm, f =15 cm, ho= 5 cm
1/u+1/v=1/f
(-1/10)+(1/v)=(1/15)
1/v=1/15+1/10
1/v=(2+3)/30
1/v =5/30
v= 6 cm

size of the image
m= hi/ho =- v/u
=- 6/10 =0.6
0.6=hi/5
hi=3 cm
The image is formed at a distance of 6 cm behind the mirror, virtual, upright and smaller than the object.

Size of the image is 3 cm.

4.6 Write in brief the basic principal of hydro-electric power generation.
Ans: Falling water spins the water turbine. The turbine drives the alternator coupled with it and converts mechanical energy into electrical energy. This is the basic “working principle of hydroelectric power plant.

4.7 A current of 1 A flows when an electric bulb is connected to 220 V mains. What could be the current when the same bulb is connected to 110V mains?
Ans: For the first case,
V₁ = 220V, I₁ =1A
R = 220/1
=220ohms

For the second phase,
V₂ = 110V, R=220ohms
I₂ = 110/220
=0.5A
Or, Find the ratio of resistance for two bulbs of 220V-60W and 110V-60W.
Ans:

4.8 Explain why a new element is formed by α-particle emission but no new element is formed by γ-ray emission from a radioactive element.
Ans: Alpha is particle whereas gamma is radiation. when alpha particles are releases from an elements there occurs a change in atomic and mass number resulting into a new element.
In gamma radiation only energy is released and hence no new elemen is formed.

4.9 Write down Dobereiner’s law of triads. Arrange Cl, Br, I, F in increasing order of their oxidising power.
Ans: Dobereiner law of triads states that, the atomic weight of the middle element of the triads was approximately equal to the arithmetic mean of those of the other two elements.
F>Cl>Br>I
Or, What is the important conclusion of Moseley’s experiment? What is the importance of this conclusion in regard to periodic table?
Ans: The Important conclusion of Moseley experiment is that the atomic number of an element is the fundamental property of an element.
On the basis of this experiment Moseley gives the modern periodic law for the periodic table.

4.10 Write two differences between the conduction of electricity through a metallic and an electrolyte during electrolysis. In electrolytic refining of copper metal, impure copper rode is used as which electrode?
Ans:

4.11 Write the names of the chemicals used and balanced chemical equation in the industrial production of urea.
Ans:

4.12 (A) and (B) are two unsaturated hydrocarbons, each containing two carbon atoms. On reaction with bromine, (A) adds one molecule of bromine per molecule and (B) adds two molecules of bromine per molecule. Write structural formula of (A) and (B). Write balanced chemical equation of reaction of (B) with bromine.
Ans:

Or, Write balanced chemical equation of the reaction of sodium hydroxide with acetic acid. Which one between jute and polythene is environment friendly for packaging and why?
Ans: NaOH + CH3COOH     →     CH3COONa   + Na
Jute is more environment friendly because it is a natural fibre so it does not do any pollution.