This reaction releases energy as heat. explain whether it obeys the law of conservation of energy.

The reaction that releases energy as heat is called an Exothermic reaction. This reaction does obey the law of conservation by preserving the energy present in the molecule and converting it to thermal heat to maintain it's from. Most reactions obey the law of conservation of energy.

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