Answer: Magnesium chloride = MgCl2
Zinc sulphide = ZnS
Sodium sulphate = Na2SO4
Calcium bicarbonate = Ca(HCO3)2
Explanation: Write down the elements side by side and their respective valencies right below. Cross multiply them to get chemical formula.
For eg: Mg Cl
2 1
Cross multiply, MgCl2
Similarly we can do the others too.
Hope you find it helpful!