The gaseous mixture used for welding of metals is

The major product of the following reaction is $P$. Number of oxygen atoms present in product $P$ is $. . . . . . . . . . . (nearest integer)$.

Given below are two statements:
Statement $I$: One mole of propyne reacts with excess of sodium to liberate half a mole of $H_2$ gas.
Statement $II$: Four $g$ of propyne reacts with $NaNH_2$ to liberate $NH_3$ gas which occupies $224 \ mL$ at $STP$.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following reagents is most suitable to distinguish compound $(3)$ from the others?
$(1) \ CH_3-C \equiv C-CH_3$
$(2) \ CH_3CH_2CH_2CH_3$
$(3) \ CH_3CH_2C \equiv CH$
$(4) \ CH_3CH=CH_2$

Acetylene gives

$Alkyne \xrightarrow[{Hg^{2+}}]{{H^+/H_2O}} \text{ketone}$
Which of the following alkynes cannot give a ketone?