Acids,Bases and Salts — Chemistry STD 10 — Question

A solution M turns blue litmus red while another solution N turns red litmus blue. In the above context answer the following questions :
(i) What do M and N must contain?
(ii) When M and N are mixed together, name one of the product formed.
(iii) When M and N are mixed together, name the other product formed.
(iv) If a piece of magnesium was put into a solution M, name the gas evolved.