\(a,HCl+NaOH\rightarrow NaCl+H_2O\\ b,n_{HCl}=\dfrac{3,65}{36,5}=0,1mol\\ n_{NaOH}=0,2.1=0,2mol\\ \Rightarrow\dfrac{0,1}{1}< \dfrac{0,2}{1}\Rightarrow NaOH.dư\\ n_{NaCl}=n_{NaOH,pư}=n_{HCl}=0,1mol\\ m_{NaOH,dư}=\left(0,2-0,1\right).40=4g\\ c,m_{NaCl}=0,1.58,5=5,85g\)