as 8 =2$^3$ so 3 bits of binary are used to represent one unit of octal
so break each unit of (123456)$_8$ into its corresponding 3 bit binary number
= (001 010 011 100 101 110)$_2$
as 16=2$^4$ so 4 bits of binary are used to represent one unit in Hexadecimal
club 4 bits of binary representation of given number from LSB and write corresponding Hexadecimal number.
=(00 1010 0111 0010 1110)$_2$ = (A72E)$_1$$_6$
as 4=2$^2$ so 2 bits of binary are used to represent one unit in 4 base number system
club 2 bits of binary representation of given number from LSB and write corresponding Hexadecimal number.
=(00 10 10 01 11 00 10 11 10)$_2$ = (22130232)$_4$
option (A)