The major product formed in the following reaction is
\(\mathrm{H}_{3} \mathrm{C}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{3}+\mathrm{Na} \xrightarrow{\text { Liquid } \mathrm{NH}_{3}}\)
1
\(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{C}=\mathrm{C}^{-} \mathrm{Na}^{+}\)
2
\(\mathrm{H}_{3} \mathrm{C}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{2}^{-} \mathrm{Na}^{+}\)
3
4