Question

Among the following, the one that has the lowest melting point is

• A. LiBr
• B. AlBr$_3$
• C. NaBr
• D. MgBr$_2$

Hint:

Compounds with more covalent character generally have lower melting points compared to ionic compounds

Answer 1

The Correct Option is B

Step 1: What controls melting point.
Strong ionic lattices melt high, while covalent molecular solids melt low.

Step 2: Spot the covalent one.
The small, highly charged aluminium ion polarises bromide strongly, so AlBr$_3$ is covalent and exists as Al$_2$Br$_6$.

Step 3: Compare.
LiBr, NaBr and MgBr$_2$ are ionic and melt high, so AlBr$_3$ melts the lowest.

Step 4: Answer.
\[ \boxed{\text{AlBr}_3} \]