An alkane gives only one monochloro derivative if all its hydrogen atoms are equivalent. This occurs in molecules with high symmetry where chlorination at any carbon produces the same compound.

For example, neopentane, $C_5{H}_{12}$, has a central carbon with four equivalent methyl groups. All 12 hydrogens are identical, so chlorination yields only one product.

Cycloalkanes like cyclopropane and cyclobutane also have all equivalent hydrogens if unsubstituted, giving a single monochloro derivative.

Final Answer: The alkanes that give only one monochloro derivative are those with all equivalent hydrogen atoms, such as neopentane and unsubstituted small cycloalkanes (from the images provided, the symmetric structures).