Step 1: Understanding the Partitioning of the Vessel
We are given that a vessel of volume \( V \) L contains an ideal gas at temperature \( T \) K. The vessel is then partitioned into two equal parts.
Step 1: Understanding the effect of partitioning
When a vessel is partitioned into two equal parts, the volume of each part will be:
\[
V' = \frac{V}{2}.
\]
Since no heat exchange occurs between the two parts after partitioning, the temperature remains the same. That is,
\[
T' = T.
\]
Step 2: Verifying the correct answer
From the above calculations, the new volume in each partition is \( \frac{V}{2} \) and the temperature remains \( T \). Hence, the correct answer is:
\[
\frac{V}{2}, T.
\]