Arrange the following compounds in the increasing order of their reactivity towards the nucleophilic addition of $HCN$:
$1. HCHO$
$2. CH_3COCH_3$
$3. PhCOCH_3$
$4. PhCOPh$

Acetone on heating with $CrO_3$ mainly forms,

Identify the product $A$ in the following reaction:
$1$-phenylcyclohex-$1$-en-$1$-one $\xrightarrow[(2) H^+]{(1) PhMgBr/CuCl} (A) (C_{19}H_{20}O)$

Identify the correct statement regarding the following sequence of reactions:
$3\text{-methylbut-1-ene}$ $\xrightarrow[(ii) NaBH_4]{(i) Hg(OCOCH_3)_2/H_2O} A$ $\xrightarrow{\Delta, H_2SO_4} B (\text{major alkene})$ $\xrightarrow{O_3/Zn} C + D$

Which of the following compounds will respond to the haloform reaction with $I_{2}$ and $KOH$?

Clemmensen's reduction will convert cyclohexanone into