In the structure of ${\text{ClF}}_3$, the number of lone pair of electrons on central atom ‘$\text{Cl}$ ’ is:

Chlorine ($\text{Cl}$) has 7 valence electrons. In ${\text{ClF}}_3$, it forms 3 single bonds with Fluorine atoms, using 3 electrons.Remaining electrons $=7-3=4$ electrons.These 4 electrons form $\frac{4}{2}=2$ lone pairs.According to VSEPR theory, the molecule has an $A{B}_3{E}_2$ type structure, resulting in a T-shape geometry.