Answer:
It was done correctly, Your answer is completely correct.
Explanation:
 
        
                    
             
        
        
        
                              2NH4ClO4 --------> N2 + Cl2 + 2O2 + 4H2O
from reaction         2 mol                              1 mol
given                     x mol                              0.10 mol
Proportion:
<u>2 mol NH4ClO4 </u>= <u>1 mol Cl2</u>
x mol  NH4ClO4   0.10 mol Cl2
x= (2*0.10)/1 = 0.20 mol NH4ClO4