In general the melting and boiling points of transition metals

Options

A. increases gradually across the period from left to right
B. decreases gradually across the period from left to right
C. first increases till the middle of the period and then decreases towards the end
D. First decreases regulary till the middle of the period and then increases towards the end.

Answer

### Step-by-Step Solution:

1. **Understanding Transition Metals**: Transition metals are elements found in the d-block of the periodic table. They are characterized by the presence of d electrons, which play a significant role in their chemical properties.

2. **Melting and Boiling Points Trend**: The melting and boiling points of transition metals generally show a trend as we move from left to right across the period.

3. **Effect of Unpaired Electrons**: As we move from left to right in the d-block, the number of unpaired electrons in the valence shell increases up to manganese (Mn). Unpaired electrons contribute to stronger metallic bonding.

4. **Behavior of Manganese**: Manganese is a special case due to its stable 3D electron configuration. The presence of a maximum number of unpaired electrons leads to a strong metallic bond, resulting in higher melting and boiling points.

5. **Trend Observation**: After manganese, the number of unpaired electrons starts to decrease. This decrease leads to a reduction in the strength of metallic bonding, which in turn causes a drop in melting and boiling points.

6. **Conclusion of the Trend**: Therefore, the general trend for the melting and boiling points of transition metals is that they increase from the left side of the d-block to the middle (up to manganese) and then decrease towards the end of the period.

### Final Answer:
In general, the melting and boiling points of transition metals increase from left to right until manganese and then decrease towards the end of the period.

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