Allred-Rochow electronegativity is given by $χ = 0.359 Z_{e ff} / r^{2} + 0.744$ with $r$ in angstrom. For an element with $Z_{e ff} = 5.45$ and covalent radius 1.10 angstrom, the value of $χ$ is nearest to

Answer: A

r^{2} = 1.21

, so

0.359 \times 5.45/1.21 = 1.617

. Adding 0.744 gives 2.36. The value 2.52 comes from forgetting to square

r

, 1.62 from omitting the constant, and 4.46 from multiplying by

r^{2}

instead of dividing.