Question

What is the general formula of halide salts of alkali metals if M is a metal atom ?

• A. \(\text{MX}\)
• B. \(\text{MX}_2\)
• C. \(\text{M}_3\text{X}_2\)
• D. \(\text{M}_2\text{X}_3\)

Hint:

Alkali metals form M+ ions and halogens form X- ions, so the halide is MX.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Alkali metals belong to group 1 and each has one electron in the outer shell. They lose that electron easily to form the \(\text{M}^+\) ion.

Step 2: Key Formula or Approach:
Halogens are in group 17. Each gains one electron to form \(\text{X}^-\). A compound must be electrically neutral, so the charges must cancel.

Step 3: Detailed Explanation:
One \(\text{M}^+\) ion carries +1 charge and one \(\text{X}^-\) ion carries -1 charge.
\[ (+1) + (-1) = 0 \]
So they combine in a 1:1 ratio and the formula is \(\text{MX}\). Examples are NaCl, KBr and LiF.
Option (B) \(\text{MX}_2\) would be formed by a +2 metal such as an alkaline earth, for example \(\text{CaCl}_2\). Options (C) and (D) would need charges like +3 or mixed charges, which alkali metals never show.

Final Answer:
Alkali metal halides have the general formula \(\text{MX}\), option (A). \[ \boxed{\text{MX (A)}} \]