Concept:
The coding rule is:
\[
m\text{ odd}\Rightarrow m^{th}\text{ letter is coded as }(m-1)^{th}\text{ letter}
\]
\[
m\text{ even}\Rightarrow m^{th}\text{ letter is coded as }(m+1)^{th}\text{ letter}
\]
We need to find the original word which gives the code
\[
\text{FZHO}
\]
Step 1: Test option GAIN.
Letters of GAIN are:
\[
G,\ A,\ I,\ N
\]
Their positions are:
\[
G=7,\quad A=1,\quad I=9,\quad N=14
\]
Step 2: Apply the coding rule.
For \(G=7\), \(7\) is odd, so code is \(7-1=6\):
\[
G\rightarrow F
\]
For \(A=1\), \(1\) is odd, so code is \(1-1\). In alphabet coding, moving one step back from \(A\) gives \(Z\):
\[
A\rightarrow Z
\]
For \(I=9\), \(9\) is odd, so code is \(9-1=8\):
\[
I\rightarrow H
\]
For \(N=14\), \(14\) is even, so code is \(14+1=15\):
\[
N\rightarrow O
\]
Step 3: Form the coded word.
\[
\text{GAIN}\rightarrow \text{FZHO}
\]
This matches the given code.
Step 4: Final answer.
\[
\boxed{\text{GAIN}}
\]