Q.2. B. Solve the following questions. (Each 2 marks)
1. Complete the following chart regarding the weight and mass of an object.
Ans.
2. State Newton’s Universal Law of Gravitation.
Ans. Gravitational force between two bodies in the universe is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
3. Define acceleration due to gravity. Write its value on the surface of Earth.
Ans. (1) The acceleration produced in a body under the influence of the force of gravity alone is called acceleration due to gravity.
(2) Its value on the surface of earth is 9.8 m/s2.
4. If a person weighs 750 N on Earth, what will be the weight of the person on moon? (The mass of moon is 1⁄8 times the mass earth and its radius is 1⁄3.7 times that of earth.)
Ans.
5. Mahendra and Virat are sitting at a distance of 1 m from each other. Their masses are 75 kg and 80 kg respectively. What is the gravitational force between them? (G = 6.67 x 10-11 Nm2/kg2)
Ans.
6) Identify the mistake in the given diagram and draw it again.
Ans.
7) The mass of planet ‘X is four times that of the earth and its radius is double the radius of the earth. The escape velocity of a body from the earth is 11.2 × 103 m/s. Find the escape velocity of a body from the planet ‘X’.
Ans.
8. State the following.
(a) Dobereiner’s Law of Triads
(b) Newland’s Law of Octaves
(c) Mendeleev’s Periodic Law
(d) Modern Periodic Law
Ans.
(a) Dobereiner’s Law of Triads: In each triad, when the elements are placed according to increasing order of their atomic masses, the atomic mass of the middle element in each triad was approximately equal to the mean of the atomic masses of the other two elements.
(b) Newland’s Law of Octaves: When the elements are arranged in an increasing order of their atomic masses, the properties of the eighth element are similar to the first.
(c) Mendeleev’s Periodic Law: The properties of elements are a periodic function of their atomic masses.
(d) Modern Periodic Law: The properties of elements are a periodic function of their atomic numbers.
9) Complete the following flow chart. 
Ans.
10) In the modern periodic table, the positions of 1 to 20 elements are shown here. Identify the elements A and B. Write their atomic number.
Ans.
(1) Element A is lithium (Li). Element B is neon (Ne).
(2) Atomic number of element A is 3. Atomic number of element B is 10.
11) Some elements and their atomic radii are given here. Arrange them in a decreasing order of their atomic radii. Identify which of the above elements is the biggest atom and which is smallest?
Ans.
(1) Decreasing order of atomic radii: Cs > Rb > K > Na> Li
(2) Cesium (Cs) has the biggest atom and lithium (Li) has the smallest atom.
12) Complete the following chart.
Ans.
13) Find the period in which these elements can be placed.
4Be, 17CI, 2He, 13Al
Ans.
(1) 4Be: Electronic configuration is (2, 2). It is placed in period 2.
(2) 17CI: Electronic configuration is (2, 8, 7). It is placed in period 3.
(3) 2He: Electronic configuration is (2). It is placed in period 1.
(4) 13Al: Electronic configuration is (2, 8, 3). It is placed in period 3.
14) Electronic configuration of element A is 2,8,1. Answer the following questions based on this information.
a) What is the atomic number of element A?
b) Find the group to which this element belongs.
Ans.
a) Atomic number of element A is 11.
b) Element A belongs to group 1.
15) Classify the following elements into Metals and Nonmetals.
S, Mg, Al, P, N, Na.
Ans:
Nonmetals: S, P, N
Metals: Mg, Al, Na
16. Explain the factors affecting the rate of chemical reaction with example. (Write any two points for 2 marks)
Ans: The factors that affect the rate of a chemical reaction are as follows:
(a) Nature of the reactants: Nature or reactivity of reactants influences the rate of a chemical reaction.
E.g. Al is more reactive than Zn. Therefore, the rate of reaction of Al with hydrochloric acid is higher than that of Zn.
(b) Size of the particles of the reactants: Smaller the size of the reactant particles, higher is the rate of the reaction.
E.g. When HCl is added to pieces of Shahabad tile, the CO2 effervescence is formed slowly. However, when HCl is added to Shahabad powder, the CO2 effervescence is formed at a faster rate.
(c) Concentration of the reactants: The rate of a chemical reaction increases with increase in the concentration of the reactants.
E.g. Dilute HCl reacts slowly with calcium carbonate, CaCO3 whereas concentrated HCl reacts rapidly with CaCO3
(d) Temperature of the reaction: Higher the temperature, faster is the rate of a chemical reaction.
E.g. The temperature in refrigerator is low. So, the rate of decomposition of perishable food stuffs is low and it remains fresh for a longer time.
(e) Catalyst: Presence of catalyst increases the rate of a chemical reaction.
E.g. The decomposition of hydrogen peroxide into water and oxygen takes place slowly at room temperature. However, the same reaction occurs at a faster rate on adding manganese dioxide (MnO2) powder in it.
17) What are reactants and products? Explain with the help of examples.
Ans:
(a) The substances taking part in chemical reaction are called reactants.
(b) The substances formed as a result of a chemical reaction by formation of new bonds are called products.
(c) Examples:
(i) Formation of carbon dioxide gas by combustion of coal in air is a chemical reaction. In this reaction, coal (carbon) and oxygen (from air) are the reactants while carbon dioxide is the product.
(ii) Decomposition of calcium carbonate by heating to form calcium oxide and carbon dioxide is a chemical reaction. In this reaction, calcium carbonate is the reactant while calcium oxide and carbon dioxide are the products.
18) Explain the following reaction with their balanced chemical equation .
a) Ammonia gas reacts with hydrogen chloride.
b) Hydrogen sulphide reacts with sulphur dioxide.
Ans.
a) Ammonia gas and hydrogen chloride gas react to form the salt ammonium chloride. It is a combination reaction.
b) Hydrogen sulphide and sulphur dioxide react to form sulphur and water. It is a redox reaction.
19) Classify the following reactions into Exothermic and Endothermic reactions.
Ans.
a) Exothermic reaction
b) Exothermic reaction
c) Endothermic reaction
d) Exothermic reaction
e) Endothermic reaction
20) Distinguish between Direct current and alternating current.
Ans.
21) How does the short circuit form?What is its effect?
Ans.
(i) The household electrical connections mainly consist of live, neutral and earth wires.
(ii) The potential difference between live and neutral wires is around 220 V.
(iii) Sometimes, due to fault in the electrical appliances or damage of the insulating coating around the two wires i.e., neutral and live, the two wires come in contact with each other and large current flows through them causing short circuit.
(iv) Large amount of heat is produced due to flow of this large current. Any inflammable material like wood, plastic, cloth, etc. present around the short circuited place can catch fire.
22) Write Fleming’s Right hand rule and Left hand rule.
Ans.
(i) Fleming’s Right hand rule: Stretch the thumb, index finger and middle finger of the right hand so that they are perpendicular to each other. If the index finger indicates the direction of magnetic field and the thumb shows the direction of motion of the conductor, then the middle finger will show the direction of induced current.
(ii) Fleming’s Left hand rule: Stretch the index finger, the middle finger and the thumb of the left hand mutually perpendicular to each other. If the index finger is in the direction of the magnetic field and the middle finger points in the direction of the current, then the thumb will point towards the direction of the force on the conductor.
23) What is an electric motor? In which appliances do we use it?
Ans.
(i) Electric motor is a device which converts electrical energy into mechanical energy.
(ii) Appliances that uses electric motor are Dryers, vacuum cleaners, fans, air conditioners, refrigerators, freezers, etc.
24) Name any two appliances which works on the phenomenon of magnetic effect of electric current.
Ans. Microphone and electric bell.
25) Name any two appliances which works on the phenomenon of heating effect of electric current.
Ans. Fuse wire and electric iron.
26) Explain the Right hand thumb rule with the help of diagram.
Ans.Right hand thumb rule : If a current carrying straight conductor is held in our right hand such that the thumb points towards the direction of current, then the curled fingers around the conductor will give the direction of the magnetic field.
27) Explain the importance of fuse wire.(Uses)
Ans.
(i) It protects circuits and appliances by stopping the flow of any excess electric current.
(ii) In summer season, when consumption of electrical power is huge in the evening due to home lighting, fan, air conditioner, use of electricity in shops etc, excessive current is drawn from the transformer. If the capacity of transformer is insufficient, its fuse wire melts and the supply gets shut down.
28) Draw a neat and labelled diagram of Hope’s apparatus.
Ans.
29) Name the following diagram appropriately.
Ans.
30) Observe the following diagram and write the answers to the questions given below.
a) Which process does the graph represent?
b) What is the range of temperature responsible for the behaviour?
Ans.
a) The graph represents anomalous behaviour of water.
b) The range of temperature responsible for the behaviour is 0°C to 4°C.