The correct option is D between 7 and 8
[H+] from HCl = 10−8 M
[H+] from H2O = 10−7 M
total [H+]=(10−8+10−7)=1.1×10−7 M
we know that pH=−log10[H+]
pH=−log10(1.1×10−7)=7−0.0414=6.9
Also, pH+pOH=14
6.9+pOH=14
pOH=14−6.9=7.1
hence, pOH of 10−8 M HCl is between 7 and 8