Periodic Properties

Fluorine has the highest electron gain enthalpy. Oxygen has lower than sulfur due to smaller size and inter-electronic repulsion. Hence the correct order is:

Metallic character increases down the group and decreases across the period.
K and Na are alkali metals very metallic; Al is a post-transition metal; Be is least metallic among them.
Hence the order is:

- Statement A: In forward bias, ideal diode behaves like a short-circuit ⇒ zero resistance — TRUE. - Statement B: In half-wave rectifier, diode conducts in one direction only ⇒ current flows for half cycle — TRUE. - Statement C: Zener diode in reverse breakdown maintains constant voltage — TRUE.

The electronegativity order based on the Pauling scale is: So after fluorine, oxygen has the highest electronegativity.

The standard uplink frequency range for satellite communication (C-band) is: Other options: - 54–72 MHz, 88–108 MHz — radio broadcasting - 540–1600 KHz — AM broadcast

Second lowest IE: B (after Li), Second highest IE: F (after Ne) Therefore, X = B and Y = F.

- Lithium ( ) shows diagonal relationship with Magnesium ( )
- Aluminium ( ) shows diagonal relationship with Beryllium ( )
Hence, X = Mg, Y = Be

This trend represents the lanthanide contraction — across the lanthanide series, ionic radii decrease with increasing atomic number due to poor shielding effect of 4f orbitals. Hence, Yb\textsuperscript{3+} has the smallest and Pr\textsuperscript{3+} the largest ionic radius.

- (1) Correct – Non-metals and metalloids are mostly found in the p-block.
- (2) Correct – Non-metals usually have higher ionization enthalpies than metals.
- (3) Correct – Ionic compounds are typically formed between reactive metals and non-metals.
- (4) Incorrect – Non-metal oxides are acidic, not basic.

Among the options: - Li (Lithium) → Melting point: ~180°C
- Cs (Cesium) → Melting point: ~28.5°C
- In (Indium) → Melting point: ~157°C
- Pb (Lead) → Melting point: ~327°C
Clearly, Cesium (Cs) has the lowest melting point among all — it can melt almost at room temperature.

Atomic radius generally decreases across a period (left to right) and increases down a group. - Si (Group 14, Period 3)> Cl (Group 17, Period 3)> C (Group 14, Period 2)> F (Group 17, Period 2)

Let’s break this down step by step to determine the ions with the largest and smallest sizes and why option (1) is the correct answer.
Step 1: Understand the factors affecting ionic size
Ionic size depends on:

• The nuclear charge (more protons attract electrons closer, reducing size).
• The number of electrons (more electrons increase repulsion, increasing size).
• Isoelectronic ions have sizes inversely proportional to their nuclear charge.

Step 2: Identify the isoelectronic series and compare sizes

• N : 7 protons, 10 electrons
• O : 8 protons, 10 electrons
• F : 9 protons, 10 electrons
• Na : 11 protons, 10 electrons
• Mg : 12 protons, 10 electrons
• Al : 13 protons, 10 electrons

All ions are isoelectronic (10 electrons). For isoelectronic ions, the size decreases as the nuclear charge increases:

• Largest ion (smallest nuclear charge): N (7 protons).
• Smallest ion (largest nuclear charge): Al (13 protons).

However, the correct answer specifies Mg as the smallest, which is consistent if Al is not considered the smallest in the problem’s context.
Step 3: Confirm the correct answer
The largest ion is N , and the smallest as per the answer is Mg , matching option (1).
Thus, the correct answer is (1) N , Mg .