Question

Across a period, the nuclear charge and the atomic radii , so the ionisation energy increases across a period.

• A. increases
• B. decreases
• C. remains same
• D. $\mathrm{increases}\mathrm{then}\mathrm{decreases}$

Answer 1

Answer: (A), (B)

decreases

The atomic number increases moving across a period and subsequently, the nuclear charge also increases. Thus, the valence electrons experience greater pull and the atomic radii decreases. As a result, more energy is required to completely extract a valence electron. Hence, ionisation energy increases across a period.