Periodic Trends In Properties Of Elements

Step 1: Ionization Energy Trend.
Ionization energy generally increases across a period from left to right due to the increasing nuclear charge. However, there are exceptions due to electron configuration, particularly in cases like nitrogen (N) and oxygen (O), where the half-filled or filled orbitals are more stable.

Step 2: Comparison of the Given Elements.
- (C) Carbon has the lowest first ionization energy because it is in the 2nd period, and it has fewer protons compared to the other elements, making it easier to remove an electron. - (N) Nitrogen has a higher ionization energy than carbon due to its half-filled stable configuration. - (O) Oxygen has a higher ionization energy than carbon but lower than nitrogen. - (F) Fluorine has the highest ionization energy due to its high electronegativity and small size.

Step 3: Conclusion.
Therefore, the element with the lowest first ionization energy is Carbon (C), corresponding to option (1).

Step 1: Allred-Rochow Electronegativity Formula.
The Allred-Rochow electronegativity ( ) is given by the formula: where is the covalent radius in Angstroms.

Step 2: Apply the Formula for Si.
For Silicon (Si), the covalent radius . Substituting the value into the formula:

Step 3: Conclusion.
Therefore, the electronegativity of Silicon (Si) is 2.20, corresponding to option (3).