4.08 g of a mixture of BaO and an unknown carbonate MCO₃ was heated strongly. The residue weighed 3.64 g. This was dissolved in 100 ml of 1 N HCl. The excess acid required 16 ml of 2.5 N NaOH solution for complete neutralization. Identify the metal M. (At wt. H = 1, C = 12, O = 16, Cl = 35.5, Ba = 138)

Complete and balance the following equation:

HNO₃ + HCl $$\to$$ NO + Cl₂

Complete and balance the following equations:

Cl₂ + OH^- $$\to$$ Cl^- + ClO^-

Elements of the same mass number but of different atomic numbers are known as ____.