If $\text{MANGO}$ is coded as $80415$, then which of the following has thus numerical code $81504$?

From the base string condition $\text{MANGO}\to 80415$, each letter matches a unique digit:
$$\text{M}=8,\text{A}=0,\text{N}=4,\text{G}=1,\text{O}=5$$

Decoding the target sequence $81504$:

* $8\to \text{M}$
* $1\to \text{G}$
* $5\to \text{O}$
* $0\to \text{A}$
* $4\to \text{N}$

The word is $\text{MGOAN}$.