Questions & explanations
1. Food cooks faster in a pressure cooker mainly because:
- (a) The cooker adds extra heat to the food
- (b) Higher pressure inside raises the boiling point of water
- (c) Steam has more chemical energy than water
- (d) The food absorbs the metal's heat directly
Answer: (b) Higher pressure inside raises the boiling point of water
Inside a sealed pressure cooker, steam is trapped and pressure rises. Higher pressure raises the boiling point of water above 100 degrees Celsius (to roughly 120 degrees Celsius), so food cooks at a higher temperature and therefore faster. The cooker does not add extra heat; it changes the boiling conditions.
2. India's Chandrayaan-3 mission is notable because it:
- (a) Was the first mission to orbit Mars
- (b) Soft-landed near the Moon's south pole in 2023
- (c) Landed humans on the Moon
- (d) Was a mission to study the Sun
Answer: (b) Soft-landed near the Moon's south pole in 2023
Chandrayaan-3 soft-landed its lander near the Moon's south polar region in August 2023, making India the first country to land near the lunar south pole and the fourth to achieve a soft Moon landing. It was an uncrewed mission. The Mars orbiter was Mangalyaan, and the solar mission is Aditya-L1.
3. In a domestic electric circuit, the fuse is connected in the:
- (a) Neutral wire
- (b) Earth wire
- (c) Live (phase) wire
- (d) All three wires equally
Answer: (c) Live (phase) wire
A fuse or MCB is placed in the live (phase) wire so that when excessive current flows due to a short circuit or overload, it breaks the live connection and cuts off the supply, preventing fire and shock. Placing it in the neutral would not safely isolate the appliance from the live supply.
4. Consider the following statements about evaporation:
1. Evaporation is a cooling process.
2. Earthen pots keep water cool because of evaporation through their pores.
Which is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither
Answer: (c) Both 1 and 2
Both statements are correct. Evaporation absorbs latent heat from the surroundings, so it is a cooling process. Earthen pots (matka) are porous; water seeps out and evaporates, drawing heat from the water inside and keeping it cool. The same principle works in desert coolers and sweating.
5. The greenhouse effect is caused mainly because greenhouse gases:
- (a) Block incoming sunlight from reaching Earth
- (b) Allow sunlight in but trap outgoing infrared heat
- (c) Cool the Earth by reflecting heat into space
- (d) Destroy the ozone layer
Answer: (b) Allow sunlight in but trap outgoing infrared heat
Greenhouse gases such as carbon dioxide, methane and water vapour are largely transparent to incoming short-wave sunlight but absorb the long-wave infrared heat radiated back by the Earth, trapping it and warming the planet. This natural effect is enhanced by human emissions.
6. We see lightning before we hear thunder because:
- (a) Light is produced before sound in a storm
- (b) Sound travels much faster than light
- (c) Light travels much faster than sound
- (d) Thunder is weaker than lightning
Answer: (c) Light travels much faster than sound
Both lightning and thunder are produced together, but light travels at about 300,000 km/s while sound travels at about 343 m/s in air. Because light is roughly a million times faster, the flash reaches us almost instantly and the sound arrives seconds later.
7. Which statement about mass and weight is correct?
- (a) Mass changes with location but weight stays the same
- (b) Weight changes with location but mass stays the same
- (c) Both mass and weight are always constant
- (d) Mass is measured in newtons and weight in kilograms
Answer: (b) Weight changes with location but mass stays the same
Mass is the amount of matter in an object and is constant everywhere, measured in kilograms. Weight is the gravitational force on that mass, measured in newtons, and changes with the strength of gravity, for example becoming one-sixth on the Moon.
8. Deficiency of which vitamin causes the disease scurvy?
- (a) Vitamin A
- (b) Vitamin C
- (c) Vitamin D
- (d) Vitamin K
Answer: (b) Vitamin C
Scurvy is caused by deficiency of Vitamin C (ascorbic acid), leading to bleeding gums and weakness. Vitamin A deficiency causes night blindness, Vitamin D deficiency causes rickets, and Vitamin K deficiency impairs blood clotting.
9. Bile, which helps in the digestion of fats, is produced by the:
- (a) Pancreas
- (b) Stomach
- (c) Liver
- (d) Small intestine
Answer: (c) Liver
Bile is produced by the liver and stored in the gall bladder. It emulsifies fats in the small intestine, breaking them into smaller droplets for enzymes to act on. The pancreas secretes digestive enzymes and insulin, but not bile.
10. On a high mountain, water boils at a temperature:
- (a) Above 100 degrees Celsius
- (b) Exactly at 100 degrees Celsius
- (c) Below 100 degrees Celsius
- (d) That does not depend on altitude
Answer: (c) Below 100 degrees Celsius
Atmospheric pressure decreases with altitude. Since the boiling point falls as pressure falls, water boils below 100 degrees Celsius on high mountains, which is why food cooks slowly there and a pressure cooker is needed.
11. Which of the following is a compound and not a mixture?
- (a) Air
- (b) Sea water
- (c) Common salt (sodium chloride)
- (d) Brass
Answer: (c) Common salt (sodium chloride)
Common salt (sodium chloride) is a compound: sodium and chlorine are chemically combined in a fixed ratio, giving it new properties. Air and sea water are mixtures, and brass is a mixture (alloy) of copper and zinc.
12. Which set correctly lists only the fat-soluble vitamins?
- (a) A, B, C, D
- (b) A, D, E, K
- (c) B, C, E, K
- (d) C, D, E, B12
Answer: (b) A, D, E, K
The fat-soluble vitamins are A, D, E and K; they are stored in the body's fat and liver. The B-complex vitamins and Vitamin C are water-soluble and are not stored, so they must be consumed regularly.