Which of the following reagents can bring about the given conversion?…

\(\text{(a) Mg-dry ether (b) }CO_2 \text{ (c) }H^+/H_2O\)

\(\text{(a) KCN (b) }H_3O^+\)

\(\text{(a) }KMnO_4 / OH^- \text{ (b) }H^+ / H_2O\)

\(\text{(a) }CrO_3/ H_2SO_4 \text{ followed by }H^+ /H_2O\)