What do the following denote?

(i) N (ii) 2N (iii) N₂ (iv) 2N₂

All of the above options are the forms of nitrogen.

(i) N denotes one atom of nitrogen.

(ii) 2N denotes two separate atoms of nitrogen

(iii) N₂ denotes one molecule of nitrogen gas.

(iv) 2N₂ denotes two molecules of nitrogen gas.