Which of the following is concentration cell

Options

A. `Cu(s) | Cu_(aq.1 M)^(2+) || Cu_(aq.1M)^(2+) |Cu(s)`
B. `Cu_(s) | Cu_(aq 0.5 M)^(2+) || Cu_(aq 0. M)^(2+) |Cu_(s)`
C. `Zn_(s) | Zn_(aq 0.5 M)^(2+) || Cu_(aq 1 M)^(2+) | Cu(s)`
D. `""^(-)Pt//H_(2)("g bar") | HCl_("aq 0.002 M") || HCl_(aq 0.005 M) | H_(2) (1 "bar") | Pt^(oplus)`

Answer

D

Explanation

`""^(-)Pt//H_(2 "g 1 bar")| HCl(aq 0.002 M) || HCl_(aq, 0.005 M) | H_(2 g 1 bar)| Pt^(oplus)`
The above cell represents similar electrode concentration but the concentration similar electrolytes (HCl) are different.
This is electrolyte concentration cell.