$CH_3-C \equiv CH \xrightarrow[dil. H_2SO_4]{HgSO_4} (A)$
$CH_3-C \equiv CH \xrightarrow[(1) BH_3.THF]{(2) H_2O_2/HO^{-}} (B)$
Products $(A)$ and $(B)$ can be differentiated by:

$[P]$ $\xrightarrow{Br_{2}} C_{2}H_{4}Br_{2}$ $\xrightarrow{NaNH_{2}/NH_{3}} [Q]$
$[Q]$ $\xrightarrow{20 \% H_{2}SO_{4}, Hg^{2+}, \Delta} [R]$ $\xrightarrow{Zn-Hg/HCl} [S]$
The species $[P], [Q], [R]$ and $[S]$ respectively are:

In the molecule $CH_3-C \equiv C-CH=CH_2$,the maximum number of carbon atoms arranged linearly is

The $C - H$ bond length is minimum in the bond formed by

The number of acidic hydrogen atoms in $but-1-yne$ is......

Which is the most suitable reagent among the following to distinguish compound $(3)$ from the others?
$(1) \ CH_3-C \equiv C-CH_3$
$(2) \ CH_3-CH_2-CH_2-CH_3$
$(3) \ CH_3-CH_2-C \equiv CH$
$(4) \ CH_3-CH=CH_2$