Which substance can be decomposed by chemical means?
(1) ammonia (3) phosphorus
(2) oxygen (4) silicon

(1) ammonia

Explanation: Ammonia is a compound which is formed by the elements nitrogen and hydrogen in a fixed ratio by mass. It can be separated into its constituent elements by chemical means.

Phosphorous (P), Oxygen (O) and Silicon (Si) are all elements and thus cannot be decomposed further.

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3