Which law is also known as law of indestructibility of matter? Why?

[LokeshCBSE]

1. Calculate the number of magnesium atoms in 3.2 g of chlorophyll, if it contains 0.024% of magnesium. [Atomic mass of Mg = 24 u]
2. Which law is also known as law of indestructibility of matter? Why?

[LokeshCBSE]

1. Amount of Mg present in 3.2 g of chlorophyll = 0.024% of 3.2 =
   Number of moles of Mg =
   1 mole of Mg contains 6.022 x 10²³
   Therefore, 3.2 x 10^–5 moles of Mg will contain 3.2 x 10^–5 x 6.022 x 10²³ = 1.93 x 10¹⁹ atoms.
2. The law of conservation of mass is also known as law of indestructibility of matter, because mass can neither be created nor be destroyed during a chemical reaction.