Question

In a period, the first ionisation enthalpy of the element at extreme left and the negative electron gain enthalpy of the extreme right element, except noble gases, are respectively.

• A. lowest and lowest
• B. highest and lowest
• C. lowest and highest
• D. highest and highest

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for trends in ionization enthalpy and electron gain enthalpy across a period in the periodic table.
Step 2: Key Formula or Approach:
- Ionization enthalpy (IE) increases across a period due to increasing nuclear charge.
- Electron Gain Enthalpy (\(\Delta_{eg}H\)) becomes more negative (higher magnitude) across a period towards halogens.
Step 3: Detailed Explanation:
1. Extreme left element (Alkali metals): They have the largest atomic size in the period and lowest nuclear charge, making it easiest to remove an electron. Thus, IE is the Lowest.
2. Extreme right element (Halogens, excluding noble gases): They have the smallest size and highest effective nuclear charge, attracting an added electron most strongly. This results in the most negative (Highest magnitude) Electron Gain Enthalpy.
Step 4: Final Answer:
The combination is lowest and highest.