0620/12 Chemistry May Jun 2015 Online Test | Cambridge IGCSE MCQ

A known mass of gaseous ammonia and excess gaseous hydrogen chloride react together to make solid ammonium chloride.
Line X shows the total mass of ammonium chloride produced over time.
The reaction is repeated at a higher pressure. All other conditions are kept the same.
Line Y shows the total mass of ammonium chloride produced over time at the higher pressure.
Which diagram is correct?