In the octal number system, each digit is represented as $\log_2 8=3$ bit binary form.
So binary representation of $(2550276)_8=(\ 010 \ 101\ 101\ 000 \ 010 \ 111 \ 110)_2$
Now we can rearrange this binary number into the group of $4$ bits to get the hexadecimal number because $\log_2 {16}=4$.
$(\ 010 \ 101\ 101\ 000 \ 010 \ 111 \ 110)_2=(\ 0000\ 1010 \ 1101\ 0000 \ 1011 \ 1110)_H=(AD0BE)_H$
Option $(C)$ is correct.