Here we are converting a binary number to octal that is we are converting a number from base 2 system to base 8 i.e. 2 3.
Hence we have to take every 3 digits from least significant bit and convert it to octal form.
for the given number 1011101011. Taking every 3 digits from LSB , we get 001 | 011 | 101 | 011 (we have appended 2 zeros at the beginning). Now 001=1; 011=3; 101=5; 011= 3. Hence answer is 1353 in octal