Consider the generic reaction between reactants a and b:
3a+4b→2c
if a reaction vessel initially contains 9 mol a and 4 mol b, how many moles of a will be in the reaction vessel once the reactants have reacted as much as possible? (assume 100% actual yield.)
how many moles of b will be in the reaction vessel once the reactants have reacted as much as possible? (assume 100% actual yield.)
how many moles of c will be in the reaction vessel once the reactants have reacted as much as possible? (assume 100% actual yield.)
express your answer using two significant figures.

Reaction:
 
3A+4B→2C

Stoichiometrial proportions:

3A : 4B : 2C

initial quantities:

9 mol A and 4 mol B.

actual ratio, 9A / 4B > theoretical ratio 3A/4B => A is in excess and B is the limiting reagent.

               Initial moles    Consumed moles    produced moles  Final moles

A              9                    3                              0                          9 - 3 = 6
B              4                    4                              0                          4 - 4 = 0
C              0                    0                              2                          2

That table contains all the answers:
 
1) how many moles of A will be in the reaction vessel once the reactants have reacted as much as possible? (Assume 100% actual yield.)

6.0 moles

2) How many moles of B will be in the reaction vessel once the reactants have reacted as much as possible? (Assume 100% actual yield.)

0.0 moles

3) How many moles of C will be in the reaction vessel once the reactants have reacted as much as possible? (Assume 100% actual yield.)

2.0 moles