Assertion (A): Aluminium cannot be extracted by electrolysing an aqueous solution of aluminium sulphate. Reason (R): Al^3+ is reduced at the cathode in preference to water because E deg(Al^3+/Al)=-1.66 V is more positive than the potential for reduction of water.

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 Advanced levelSingle correct optionDifficulty 3 of 3mt150

Assertion (A): Aluminium cannot be extracted by electrolysing an aqueous solution of aluminium sulphate. Reason (R): $Al X^{3 +}$ is reduced at the cathode in preference to water because $E^{\circ} (Al X^{3 +} / Al) = - 1.66 V$ is more positive than the potential for reduction of water.

In aqueous solution water (about

- 0.41 V

at pH 7) is reduced to

H X_{2}

before

Al X^{3 +}

because

- 1.66 V

is much more negative, so no aluminium deposits. A is true. R is false since

- 1.66 V

is more negative, not more positive, than that of water.