Answer
%Yield = 29%
Step-by-step explanation
Given
2 Na + Cl2 --> 2 NaCl
moles of Na = 21 mol
moles of Cl2 = 21 mol
theoretical moles of NaCl = 21 moles
actual moles of NaCl = 6 moles
Solution
%Yield = actual/theoretical x 100
%Yield = 6 mol/21 mol x 100
%Yield = 29%