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Question:

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

1:2:3

3:2:2

1:3:2

2:3:1

Solution:

Number of moles of X, Y and Z are
4.2/7 : 5.4/27 : 19.2/64
are 0.6 : 0.2 : 0.3
So, 6 : 2 : 3
since same current is passed so there number of equivalence will be same.
So, using that concept gives the ratio's of valence 1:3:2