$($ Carry of $n-1^{th}$ $\oplus$ Carry of $n^{th}) = 1$ Then overflow in 2's complement
$\text{Format of a number here}:\color{green} {C_4}\color{red}{C_3}C_2C_1C_0$
In above format $C_4$ is $n^{th}$ carry
$(i) \space 1100 +1100 = 1000 $ Here $C_{n-1} = 1 , C_n = 1$ so $C_{n-1}\oplus C_n = 1 \oplus 1 = 0$
$(ii) \space 0011 +0111 = 1010 $ Here $C_{n-1} = 1 , C_n = 0$ so $C_{n-1}\oplus C_n = 1 \oplus 0 = 1$
$(iii) \space 1111 +0111 = 0110 $ Here $C_{n-1} = 1 , C_n = 1$ so $C_{n-1}\oplus C_n = 1 \oplus 1 = 0$
So option $B$ is only right choice