Periodic Table

Step 1: Analyze periodic trends.
- Metallic radius increases as we go down the group because the atoms get larger due to the addition of electron shells.
- Melting point and boiling point decrease as we move down the group because the metallic bonds weaken due to increased atomic size.
- Density increases, not decreases, as you go down the group because the atoms get larger and more massive.
- Ionization energy decreases as we move down the group because the outermost electron is farther from the nucleus and more shielded by inner electrons.
Step 2: Conclusion. Thus, the correct options are (A), (B), and (D).
Final Answer:

Step 1: Identifying the element.
Mendelevium (Md) is a synthetic element in the actinide series of the periodic table.
Step 2: Atomic number.
Mendelevium has an atomic number of 101.

Final Answer:

Step 1: Ionization energy trend.
Ionization energy increases across a period (from left to right) because the atomic size decreases, leading to a stronger attraction between the nucleus and the electrons. Ionization energy decreases down a group because the outermost electrons are farther from the nucleus and more shielded by inner electrons.
Step 2: Analyze the elements.
- Lithium (Li) has the lowest ionization energy because it is in Group 1.
- Boron (B) has a higher ionization energy than Li but less than Be and C.
- Beryllium (Be) has a higher ionization energy due to its stable electron configuration.
- Carbon (C) has the highest ionization energy because it is farther across the period and has a relatively small atomic size.
Step 3: Conclusion.
The order of increasing first ionization energy is:
Final Answer:

Step 1: Recall Group 13 elements.
Group 13 (B, Al, Ga, In, Tl) usually show +3 oxidation state.
Step 2: Inert pair effect.
In heavier elements (like Tl), the ns electrons become reluctant to participate in bonding due to poor shielding and relativistic effects. This causes a stable +1 oxidation state (monovalency).
Step 3: Conclusion.
Thus, the occurrence of monovalency in Group 13 is explained by the inert pair effect.
Final Answer: