B KOH
I would say this is the base for the compound substance
(20/23) times 100 is 87%
now the answer asks for percentage ERROR
100-87 =13
so answer is C
C can be the only correct answer - 6.023 x 10^23 is the amount of molecules in a mol of an element. 4.5 x 6.023 x 10^23 can not equal anything but C.
4.5 x 6.023 x 10^23 = 2.71035 x 10^24
Bit.my/3a8Nt8n here’s the link for the answer