According to the ideal gas law, \( PV = nRT \). If the volume \( V \) is held constant and the temperature \( T \) increases, the pressure \( P \) must increase in order to maintain the equality. This is because \( n \) (the number of moles of gas) and \( R \) (the ideal gas constant) are also constants.
Thus, the correct response is:
It would increase.