1. Recall the condition for chirality

A compound is chiral if it is not superimposable on its mirror image. In simple alkyl halides, this usually happens when there is a carbon atom attached to four different groups (a stereogenic center).

We will check each option for the presence or absence of such a carbon.

2. Option A: 1-chloropentane

Structure: $\mathrm{Cl{-}CH_2{-}CH_2{-}CH_2{-}CH_2{-}CH_3}$

The carbon attached to chlorine is a $\mathrm{CH_2}$ carbon, so it has two identical hydrogens.

No carbon in this molecule has four different substituents.

Therefore, 1-chloropentane is achiral.

3. Option B: 3-chloro-2-methylpentane

Structure: $\mathrm{CH_3{-}CH(CH_3){-}CH(Cl){-}CH_2{-}CH_3}$

Check carbon-3:

• $\mathrm{Cl}$
• $\mathrm{H}$
• left side: $\mathrm{-CH(CH_3)CH_3}$
• right side: $\mathrm{-CH_2CH_3}$

These are four different groups, so carbon-3 is a stereogenic center.

Hence, this compound is chiral.

4. Option C: 1-chloro-2-methylpentane

Structure: $\mathrm{ClCH_2{-}CH(CH_3){-}CH_2{-}CH_2{-}CH_3}$

Check carbon-2:

• $\mathrm{H}$
• $\mathrm{CH_3}$
• $\mathrm{CH_2Cl}$
• $\mathrm{CH_2CH_2CH_3}$

These are four different groups, so carbon-2 is a stereogenic center.

Hence, this compound is chiral.

5. Option D: 2-chloropentane

Structure: $\mathrm{CH_3{-}CH(Cl){-}CH_2{-}CH_2{-}CH_3}$

Check carbon-2:

• $\mathrm{Cl}$
• $\mathrm{H}$
• $\mathrm{CH_3}$
• $\mathrm{CH_2CH_2CH_3}$

Again, four different groups are attached.

Hence, this compound is chiral.

6. Conclusion

Only Option A does not have any stereogenic center and is therefore not chiral.

$\boxed{\text{A: 1-chloropentane}}$

7. Comparison with stored correct answer

Stored correct answer: A

My derived answer: A

So, the derived answer agrees with the stored correct answer.