What is the valency of nitrogen in :

(i) NO

(ii) N₂O

(iii) NO₂

Name a non-metallic element, which :

(a) is liquid at ordinary temperature

(b) is a conductor of electricity

Name the process of change of state by which napthalene changes into vapour. Name an element that can undergo the same change of state.

Dilute hydrochloric acid is added first to a mixture of iron and sulphur and then to a compound formed by iron and sulphur. Name the gases formed in each case.