The chemical formula for manganese(II) chlorate is Mn(ClO3)2. Mn is the chemical symbol for magnesium, Cl is the chemical symbol for chlorine and O is the chemical symbol for oxygen. The chemical formula for chlorate is ClO3.
The Roman numeral II after manganese refers to the +2 charge of the manganese ion. The chlorate ion has a charge of -1, so the formula requires two ions of chlorate to balance out the +2 charge of the manganese and create a molecule with a neutral charge. The 2 after the parenthesis indicates two atoms of chlorine and six atoms of oxygen.