1. Determine the central atom and valence electrons

In $\mathrm{ClF_5}$, chlorine is the central atom.

• Valence electrons on $\mathrm{Cl} = 7$
• Each fluorine contributes one bond.

So chlorine forms $5$ sigma bonds with $5$ fluorine atoms.

2. Count lone pairs on chlorine

Chlorine has $7$ valence electrons. Out of these, $5$ are used in bonding with $5$ fluorine atoms, leaving:

$7 - 5 = 2 \text{ electrons}$

These $2$ electrons form one lone pair.

Thus, around chlorine there are:

• $5$ bond pairs
• $1$ lone pair

Total electron pairs $= 6$.

3. Find electron pair geometry using VSEPR theory

For $6$ electron pairs, the electron pair geometry is octahedral.

4. Find molecular shape

In an octahedral arrangement, if one position is occupied by a lone pair, the molecular shape becomes:

$\text{Square pyramidal}$

So, $\mathrm{ClF_5}$ has square pyramidal geometry.

5. Determine physical state at room temperature

$\mathrm{ClF_5}$ is known to be a colourless liquid at room temperature.

6. Match with options

• A: Colourless liquid with square pyramidal geometry ✅
• B: Colourless gas with square pyramidal geometry ❌
• C: Colourless gas with trigonal bipyramidal geometry ❌
• D: Colourless liquid with trigonal bipyramidal geometry ❌

Therefore, the correct option is:

$\boxed{\text{A}}$

7. Comparison with stored correct answer

Stored correct answer: A

My derived answer: A

They match.