N2O4 ↔ 2NO2
The following system react as below when increase in pressure occurs
The equilibrium will shift towards the left (more N2O4 is produced)
Explanation
When pressure increases the equilibrium shift toward the side of reaction with fewer moles of gas.
In the reaction of N2O4 ↔ 2 NO2 there is only 1 moles of N2O4 and 2 moles of NO2.
Therefore increase in pressure led to shift of equilibrium towards the left. ( more N2O4 is produced)