What is the white powder formed when a piece of magnesium is burned in air?

A piece of magnesium is burned in air.

$\mathrm{Mg}+{\mathrm{O}}_2\to \mathrm{MgO}$

Which are the reactants and products here?

A piece of magnesium is burned in air.

$\mathrm{Mg}+{\mathrm{O}}_2\to \mathrm{MgO}$

Note down the number of atoms in the reactant side and the number of atoms in the product side in the table below.

Is the number of atoms of each element equal on both sides?

The number of which atom is not equal on both sides?

A piece of magnesium is burned in air.

$\mathrm{Mg}+{\mathrm{O}}_2\to \mathrm{MgO}$

How many product molecules are needed to equalize the number of oxygen atoms on both sides?

$\mathrm{Mg}+{\mathrm{O}}_2\to 2\mathrm{MgO}$

Is the number of magnesium atoms equal on both sides?

How many magnesium atoms are needed in the reactant side to equalize the number of magnesium atoms on both sides?

$2\mathrm{Mg}+{\mathrm{O}}_2\to 2\mathrm{MgO}$

Is the total number of atoms and mass of each element in the molecules present in the reactant side and that in the product side equal in this equation? 

$\mathrm{Zn}+\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$

How many Zinc atoms are there in the reactant side and in the product side? Which are the atoms showing a difference in their number?

In order to make equal number of atoms on both sides how many molecules of $\mathrm{HCI}$ should be taken as reactant.

$\mathrm{Zn}+\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$