N2+3H2<--->2NH3
Decreasing nitrogen:
Increases or decreases hydrogen? Increases or decreases ammonia?
Decreasing hydrogen :
Increases or decreases nitrogen? Increase or decreases ammonia?
In a not so esoteric statement, Le Chatelier's Principle says that an equation in equilibrium tries to UNDO what we do to it. Therefore, if we take away N2 the reaction will shift so as to increase N2. That means it shifts to the left which means H2 increases.
It also means NH3 decreases.