Answer
2.4 L
Work Step by Step
As the temperature and pressure are same, the ratio of volumes of the molecules in the reaction $N_{2}+3H_{2}→2NH_{3}$ is equal to the ratio of the number of moles which is 1:3→ 2.
Here, $1\times1.2L + 3\times 1.2 L $→ Volume of $NH_{3}$
Implies, the volume of $NH_{3}$ formed = $2\times1.2 L$ = 2.4 L