Q1: Binary subtraction of a decimal 15 from 43 will utilize which two's complement?

ANS:D - 110001

I think answer will be (C).

43 = 1 0 1 0 1 1.
15 = 0 0 1 1 1 1.

Take the 2's complement of 15 =1 1 0 0 0 1.

Then add this value with binary equivalent of 43.

Will get,

1 0 1 0 1 1
+1 1 0 0 0 1
=1 0 1 1 1 0 0.

Then discard the carry output you will get 011100 so option will be (C).
We can verify it by taking simply 43 - 15 = 28.

When you will convert option C in decimal number that will give the correct answer that is '28'.