(i) Of what lead pencils are made of?
Ans: Lead pencils are made of graphite. Before the discovery of graphite, soft metals like lead were used for writing. An old name of graphite was 'black lead' and henced the name lead pencils.


(ii) Why is one’s breath visible in cold but not in hot weather?
In cold weather, vapours in exhaled breath take the form of tiny droplets due to cold and thus they become visible.

(iii) What is the chemical composition of diamond?
Ans: Diamond is composed solely of carbon with traces of impurities like boron and nitrogen.

(iv) Name the vaccine that protects against tuberculosis.
Ans: BCG Vaccine. BCG stands for Bacillus Calmette Guerin

(v) Name the disease of the liver that causes a patient to turn yellow.
Ans: Jaundice