A metal M forms an alum which contains the element potassium and is isomorphous with ordinary alum`(K_2SO_4. Al_2(SO_4)_3 24H_2O)` . If the alum of M contains 10.42% of M, then atomic weight of M is (at. mass of K= 39, O=16, S=32 and H=1):

Options

A. 52
B. 104
C. 156
D. 208

Answer

A

Explanation

Since the alum is isomorphous with `K_2SO_4`
`Al_2(SO_4)_3.24H_2O ` its formula is `K_2SO_4`.
`M_2(SO_4)_3 . 24 H_2O`
Molecular weight = 894 + 2M where M is the atomic weight of the metal
Now ` (2M)/(894 + 2M) xx 100 = 10.42 `
solving M = 52