$(734)_{8}=(...)_{16}$
First Convert Octal to Binary.
$8=2^{3}\implies$Write $3$-bit binary number for each digit.
$(734)_{8}=(111\:011\:100)_{2}$
Now we know that $2^{4}=16\implies$ Make a group of $4$-bit from LSB to MSB , and at MSB we can add zeros if required. And write the hexadecimal number from each group of $4$-bit binary number.
$(111\:011\:100)_{2} = (0001\:1101\:1100)_{2}=(1\:D\:C)_{16}$.
$\implies$ Hexadecimal number representation are follows this$:0,1,2,3,4,5,6,7,8,9,A(10),B(11),C(12),D(13),E(14),F(15)$
So,the correct answer is $(D)$.