AIIMS 2015 Chemistry Question Paper for free online practice with solutions

Salts of metals X, Y and Z are electrolysed under identical condition using same quantity of electricity. It was observed that 4.2 g of X, 5.4 g of Y and 19.2 g of Z were deposited at respective cathode. If the atomic weights of X,Y, Z are 7, 27 and 64 respectively, then their ratio of valencies is