Step 1: Charge balance:
Group 1 metals have a single stable oxidation state of $+1$. Halide ions have charge $-1$.
Step 2: Combine:
To make the total charge zero, we need equal numbers of each ion, giving ratio $1:1$. So the formula is $\text{MX}$.
Step 3: Rule out the others:
$\text{MX}_2$ needs $\text{M}^{2+}$, found in group 2. $\text{M}_3\text{X}_2$ would need $\text{M}^{2+}$ with a $-3$ anion, and $\text{M}_2\text{X}_3$ needs $\text{M}^{3+}$ with $\text{X}^{2-}$. Neither is possible for alkali metals and halides.
Final Answer:
General formula is $\text{MX}$, option (A).
\[ \boxed{\text{MX (A)}} \]