Consider the following equation:
4nh₄ + 5o₂ → 4 no + 6h₂o
how many moles of water are produced when 2 moles of nh4 react with excess oxygen gas?

See we have two moles of NH4, so we replace 4 NH4 by 2 NH4.
Now, on balancing the equation, we get 2 NH4 + 3O2 ---> 2NO + 4 H2O (law of conservation of mass)
thus, 2 moles of NH4 react with 3 moles of oxygen gas to produce 2 moles of NO2 and 4 moles of H2O.
Thus, we get 4 moles of H2O 

There is one s orbital, and there are three p orbitals, five d orbitals, and seven f orbitals. thus, the answer is b. do not confuse the number of orbitals in a subshell with the number of electrons the subshell can hold. each orbital can hold two electrons, so the capacity of an nf subshell is 14 electrons.