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We should protect the water of ponds and lakes from being contaminated by washing of clothes, bathing of humans and animals, throwing of garbage in water.

1. Due to anomalous behaviour of water, in cold countries, water changes to ice. 

2. Due to this change, its volume increases and density decreases. So ice floats on water. 

3. Ice is a bad conductor of heat so it doesn’t allow heat to go inside so the water below ice remains as it is. So aquatic animals remain alive even after the rivers or lakes freeze in winter.

1. Due to anomalous behaviour of water, in cold countries when water gets cool and turn to ice, its volume increases, so its density decreases 

2. Due to less density ice floats on water. 

3.  (a) Ice is a bad conductor of heat and electricity, (b) It doesn’t allow outside heat to go from the ice to water so water temperature below the ice doesn’t change, (c) It remains as water so aquatic animals remain alive even after the rivers or lakes freeze in winter.

The jerk to the thermometer will allow the mercury level to flow into the bulb so that the mercury level is below the normal temperature.

Similarities between laboratory thermometer and the clinical thermometer:

1. Both clinical and laboratory thermometers have long, narrow and uniform glass tubes.

2. Bulbs contain mercury. 

3. Both have Celsius scale.

Differences: 

Laboratory thermometer:

1. Laboratory thermometer is generally scaled from -10°C to 11 CPC. 

2. Mercury level falls on its own as no kink is present. 

3. Temperature is read while keeping the thermometer in the source of temperature, e.g. a liquid or any other thing. 

4. No need to give jerk to lower the mercury level. 5. It is used to take temperature in laboratory.

Clinical thermometer: 

1. Clinical thermometer is scaled from 35°C to 42°C or from 94°F to 108°F. 

2. Mercury level does not fall on its own, as there is a kink near the bulb to prevent the fall of mercury level. 

3. Temperature can be read after removing the thermometer from armpit or mouth. 

4. To lower the mercury level jerks are given. 

5. It is used for taking the body temperature.

It is wrong, because clinical thermometer has small temperature range (35°C to 42°C or 94°F to 108°F). If it is used to measure the temperature of hot water, the glass will crack/ burst due to excessive pressure created by expansion of mercury.

Use of Digital thermometer: 

1. Wash the tip with warm (not hot), soapy water. 

2. Press the “ON” button.

3. Insert the tip of the thermometer into the mouth, bottom, or under the armpit. 

4. Hold the thermometer in place until it beeps (about 30 seconds). 

5. Read the display. 

6. Turn off the thermometer, rinse under water, and put it away in a safe place.

Digital Thermometer: 

1. Mercury is a toxic substance and is very difficult to dispose of if a thermometer breaks. 

2. These days, digital thermometers are available which do not use mercury.

3. Instead, it has a sensor which can measure the heat coming out from the body directly and from that can measure the temperature of the body. 

4. Digital thermometers are mainly used to take the body temperature. 

5. Do not use a clinical thermometer for measuring the temperature of any object other than human body. 

6. Avoid keeping it in the sun or near of flame.

(a) Laboratory Thermometers: 

1. Laboratory thermometers are used to measure the temperature in school and other laboratories for scientific research. 

2. They are also used in the industry as they can measure temperatures higher than what clinical thermometers can record. 

3. The stem and the bulb of a lab thermometer are longer when compared to that of a clinical thermometer and there is no kink in the lab thermometer. 

4. A laboratory thermometer has only the Celsius scale ranging from -10°C to 110°C.

(b) Precautions to be Followed While Using a Laboratory Thermometer:

1. Do not tilt the thermometer while measuring the temperature. Place it upright. 

2. Note the reading only when the bulb has been surrounded by the substance from all sides.

1. Take some water in a beaker. 

2. Take a laboratory thermometer and immerse its bulb end in water; holding it vertically. Ensure to dip whole portion of bulb end. The bulb end should not touch the bottom or side of the beaker. 

3. Observe the movement of rise of mercury. When it becomes stable, take the reading of the thermometer.

4. Repeat this with hot water and take the reading.

(c) Celsius scale

The gas deviates from ideal behaviour. When more gas is introduced to the container at constant temperature, the number of molecules in the container will increase. This will result in increase in the attractive forces between the molecules and hence the gas will deviate from ideal behaviour.

(c) laboratory thermometer

The gas behaves ideally. When the temperature of the gas is raised at constant pressure, its volume increases. Due to increase in the volume of gas, the attractive forces between molecules decrease and the actual volume occupied by the molecules may become negligible as compared to the total volume of the gas. Under these conditions, the gas behaves ideally.

Correct answer is (d) 35°C to 42°C

X is carbon (non-metal). X exists in the form of allotropes, Y is diamond and Z is Graphite.

(i) X - Carbon, Y - Diamond, Z - Graphite

(ii)Non-metal

(iii)Tin.

(i) Deficiency of iodine leads to goitre. It also leads to hypothyroidism, a most common disease among ladies above 40 years of age.

(ii) Graphite is a non-metal which is a good conductor of heat and electricity.

(iii) suggestions :

(a)  To start an awareness campaign in localities, homes and schools.

(b) To make understand the importance of iodine heat and electricity. to people

When a metallic oxide is dissolved in water, the solution formed has a high concentration of OH” ions. 

Dilution of concentrated acid is an exothermic process. If Water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. When the acid is added to water slowly with constant stirring, the mixture will not splash out.

Yes, non-metallic oxide is acidic in nature. It reacts with base and forms salt and water.

Mixing water to acid is an exothermic reaction. Hence while diluting an acid it is recommended that the acid should be added to water and not water to acid. If we mix water to acid explosion occurs and burning take place.

1. Dry hydrogen chloride gas is not an acid. Hence it can’t turn blue litmus into red. 

2. Hydrochloric acid is an aqueous solution. Hence it can turn blue litmus into red.

Dry HCI gas does not change the colour of dry litmus paper because it has no hydrogen ions (H⁺) in it.

(i) Solid sodium chloride and conc. sulphuric acid.

(ii) Dry litmus - no change

Wet blue litmus - changes to red

(iii) HCl +H₂O→H₃O⁺ +Cl^-  

H₃O⁺   - (Hydronium ion)

Cl^-  -(Chloride Ion)

Correct answer is (a) 400 N

(c) product of mass and acceleration

(b) on the surface of earth

(c) reduced to one-fourth

(b) escape velocity

Correct answer is (c) 15 N

Correct answer is (b) maximum

(b) at centre of the earth

(d) a force always acts on it

Correct answer is (d) space

(c) varies with the latitude on earth

As F = ma so for given a, more force will be required to put a large mass in motion.

Correct answer is (c) zero

Ratio of masses m₁ : m₂ = 3 : 4 

Acceleration of m₂ is a₂ = 12 m/s²

Force acting of m₂ is F₂ = m₂ a₂

F₂ = 4 × 12 = 48N 

but F₂ = F₁ 

∴ Force acting on m₁ is F₁ = 48N 

∴ Acceleration of m₁ = a₁ =\(\frac{F_1}{m_1}\) 

a₁ = \(\frac{48}{3}\) 

= 16 m/s² 

Acceleration of the other body ax = 16 m/s²

Correct answer is (c) Kinematics

Correct answer is (d) F × d

(a) is opposite to the direction of motion

(a) decreases

Common forces in mechanics : 

(i) Weight : Weight of an object is the force with which earth attracts it. (W = mg) 

(ii) Reaction or Normal force : When a body is placed on a rigid surface, the body experience a force which is perpendicular to the surfaces in contact. Then force is called ‘Normal force’ or ‘Reaction’. 

(iii) Tension : The force exerted by the end of taut string, rope or chain against pulling (applied) force is called the tension. The direction of tension is so as to pull the body. 

(iv) Spring force : Every spring resists any attempt to change its length. This resistive force increases with changes in length. Spring force is given by F = – Kx; where x is the change in length and K is the spring constant (unit N/m).

To reduce friction and so to reduce wear & tear.

(a) P = m × v

1. True 

2. False – Apparent weight of a person is not always equal to his actual weight. 

3. False – Weight of a body is minimum at the equator. It is maximum at the poles. 

4. False – Turning a nut with a spanner having a longer handle is so easy than one with a short handle. 

5. False – Astronauts are falling freely around the earth due to their huge orbital velocity.

1. (b) both the assertion and the reason are true and the reason is the correct explanation of assertion.

 2. (c) Assertion is true, but the reason is false.

Correct answer is (c) Nm²/g²

Correct answer is (c) ms^-2