Chromium plating can involve the electrolysis of an electrolyte of an acidified mixture of chromic acid and chromium sulphate. If during electrolysis the article being plated increases in mass by `2.6g` and `0.6dm^(3)` of oxygen are evolved at an inert anode, the oxidation state of chromium ions being discharged must be `: (` assuming atomic weight of `Cr=52` and `1 mol e` of gas at room temperature and pressure occupies a volume at `24dm^(3))`

Options

A. `-1`
B. Zero
C. `+1`
D. `+2`

Answer

D

Explanation

Wt. of `O_(2) = ("Molar mass" xx "Vol"(dm^(3)))/(22.4)`
`= (32xx 0.6)/(22.4) = 0.86` g
A/c. to Faraday's `II^(nd)` law
`(W_(Cr))/(E_(Cr)) = (W_(O_(2)))/(E_(O_(2)))`
`(2.6)/(52//n) = (0.86)/(8) " " [ because E = ("Molar mass")/("oxidation state")]`
`therefore n = (0.86 xx 52)/(8 xx 2.6) -= 2`
or `(2.6)/(52//n) = (0.6 xx 4)/(24)`
`therefore n = 2`