21. The gas present in the stratosphere which filters out some of the sun’s ultraviolet light and provides an effective shield against radiation damage to living things is
A. helium
B. ozone
C. oxygen
D. methane
Answer:
B. ozone

22. The most commonly used bleaching agent is
A. alcohol
B. carbon dioxide
C. chlorine
D. sodium chlorine
Answer:
C. chlorine

23. The nucleus of a hydrogen atom consists of
A. 1 proton only
B. 1 proton + 2 neutron
C. 1 neutron only
D. 1 electron only
Answer:
A. 1 proton only

24. The heat required to raise the temperature of body by 1 K is called
A. specific heat
B. thermal capacity
C. water equivalent
D. None of the above
Answer:
B. thermal capacity

25. The nuclear particles which are assumed to hold the nucleons together are
A. electrons
B. positrons
C. neutrons
D. mesons
Answer:
D. mesons

26. Which substance is used to retard the setting action of cement?
A. CaO
B. AlO
C. CaSO.2HO
D. NaO + KO
Answer
C. CaSO.2HO

27. What is a mixture of potassium nitrate , powdered charcoal and sulphur called?
A. Glass
B. Cement
C. Paint
D. Gun Powder
Answer
D. Gun Powder

28. Which one of the following is the softest?
A. Iron
B. Aluminium
C. Calcium
D. Lithium
Answer
A. Iron

29. The iron layered with zinc is called
A. Pig iron
B. Cost iron
C. Galvanised iron
D. Steel
Answer
C. Galvanised iron

30. When quick lime is added to water
A. Heat is liberated
B. Heat is absorbed
C. Temperature decreases
D. No heat change takes place
Answer
A. Heat is liberated

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