Assertion (A): A paper moistened with acidified potassium dichromate turns green in both SO2 and H2S. Reason (R): Both gases are reducing agents that reduce Cr(VI) to Cr(III).

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is not the correct explanation of A

JEE Main levelSingle correct optionDifficulty 2 of 3qa174

Assertion (A): A paper moistened with acidified potassium dichromate turns green in both $SO X_{2}$ and $H X_{2} S$ . Reason (R): Both gases are reducing agents that reduce $Cr (VI)$ to $Cr (III)$ .

SO X_{2}

reduces dichromate as

Cr X_{2} O X_{7} X^{2 -} + 3 SO X_{2} + 2 H X^{+} 2 Cr X^{3 +} + 3 SO X_{4} X^{2 -} + H X_{2} O

and

H X_{2} S

Cr X_{2} O X_{7} X^{2 -} + 3 H X_{2} S + 8 H X^{+} 2 Cr X^{3 +} + 3 S + 7 H X_{2} O

. Green

Cr X^{3 +}

appears in both cases because both gases are reductants, so A and R are true and R explains A.