Identify the reaction being asked

Sodium in liquid ammonia is used to react with compounds having an acidic hydrogen attached to a triple-bonded carbon.

Terminal alkynes, of the type $R-C\equiv C-H$ contain an acidic hydrogen and can react with sodium to form sodium acetylide: $2R-C\equiv C-H + 2Na \rightarrow 2R-C\equiv C^{-}Na^{+} + H_2$

So, we need to find the terminal alkyne among the options.

Check each option

Option A: $CH_3CH_2CH_2C\equiv CCH_2CH_2CH_3$

• Triple bond is in the middle of the chain.
• Structure is of the form $R-C\equiv C-R'$.
• This is an internal alkyne.
• No acidic terminal hydrogen.
• Does not react with sodium in liquid ammonia in this way.

Option B: $CH_3CH_2C\equiv CH$

• Triple bond is at the end.
• Structure is of the form $R-C\equiv C-H$.
• This is a terminal alkyne.
• Has acidic hydrogen on the terminal carbon.
• Reacts with sodium in liquid ammonia.

Option C: $CH_3CH=CHCH_3$

• This is an alkene.
• No terminal alkyne hydrogen.
• Does not react in the required way.

Option D: $CH_3CH_2C\equiv CCH_2CH_3$

• Triple bond is internal.
• Structure is $R-C\equiv C-R'$.
• Internal alkyne.
• No acidic terminal hydrogen.
• Does not react with sodium in liquid ammonia in this context.

Conclusion

Only Option B is a terminal alkyne and hence reacts with sodium in liquid ammonia.

Therefore, the correct answer is: $\boxed{B}$

Comparison with stored correct answer

Stored correct answer: B

My derived answer: B

Hence, they agree.