B) How does electron gain enthalpy change along a period and in a group?

Electron gain enthalpy becomes more and more negative from left to right in a period. As we move across a period from left to right the atomic size decreases and the nuclear charge increases

Variation in electron gain enthalpy in the period : in the modern periodic table, on moving from left to right across a period the atomic size of elements decreases and the effective nuclear charge increases.

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Explanation:

Option (b) is the correct answer.

Explanation:

When we move from left to right across a period in a periodic table then there will occur a decrease in size of the atoms because electrons are added to the same shell.

As a result, nucleus tends to pull the electrons towards itself due to which shrinkage in the size of atoms tends to occur.

Thus, we can conclude that atomic radius tends to decrease from left to right across a period in the periodic table.