Question

Within each pair of element F & Cl, S & Se, and Li & Na, respectively, the elements that release more energy upon electron gain are

• A. Cl, S and Li
• B. F, S and Li
• C. Cl, Se and Na
• D. F, Se and Na

Answer 1

Answer: (A)

$Cl>F$ (in case of fluorine addition of electron becomes little tough than chlorine so electron affinity is less than chlorine it is due to more electron density and smaller size of fluorine atom which causes more electron repulsion)
$S>Se$ and $Li>Na$ (as on moving down the group size increases, and effective nuclear charge decreases so electron affinity decreases.