21.The most abundant gas in the Earth's atmosphere is.

Ans:Nitrogen

22.The pH value of pure water is.

Ans:7 (neutral)

23.Which gas is released during photosynthesis?

Ans:Oxygen

24.The lightest element in the periodic table is.

Ans:Hydrogen

25.Rust is chemically known as.

Ans:Iron oxide

26.Which acid is present in the human stomach?

Ans:Hydrochloric acid

27.The chemical name of baking soda is.

Ans:Sodium bicarbonate

28.Diamond and graphite are allotropes of.

Ans:Carbon

29.The powerhouse of the cell is.

Ans:Mitochondria

30.The basic structural and functional unit of life is.

Ans:Cell

31.The largest organ of the human body is.

Ans:Skin

32.The number of bones in an adult human body is.

Ans:206

33.Which vitamin is produced in the body when exposed to sunlight?

Ans:Vitamin D

34.The red colour of blood is due to.

Ans:Haemoglobin

35.Which part of the plant conducts photosynthesis?

Ans:Leaf (chloroplast)

36.The deficiency of which vitamin causes scurvy?

Ans:Vitamin C

37.The human heart has how many chambers?

Ans:Four

38.Insulin is produced by which organ?

Ans:Pancreas

39.The gas responsible for the greenhouse effect is mainly.

Ans:Carbon dioxide

40.The ozone layer protects the Earth from.

Ans:Ultraviolet radiation