On moving down the group 13 density

Options

A. Increase
B. Decrease
C. First decreases then increases
D. Remains same

Answer

### Step-by-Step Solution:

1. **Identify the Group**: We are focusing on Group 13 of the periodic table, which includes the elements: boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl).

2. **Understand Atomic Size**: As we move down Group 13 from boron to thallium, the atomic size (or atomic radius) increases. This increase is due to the addition of electron shells as we progress down the group.

3. **Consider Atomic Mass**: Along with the increase in atomic size, the atomic mass of the elements also increases as we move down the group. This is because each subsequent element has more protons and neutrons in its nucleus.

4. **Density Calculation**: Density (D) is defined as mass (m) divided by volume (V):
\[ D = \frac{m}{V} \]
As atomic mass increases, the mass component of the density formula increases.

5. **Volume Consideration**: While the volume of the atoms also increases due to the larger atomic size, the increase in mass is more significant than the increase in volume for these elements.

6. **Conclusion on Density**: Therefore, as we move down Group 13, the density of the elements generally increases because the increase in mass outweighs the increase in volume.

7. **Final Answer**: The density of Group 13 elements increases as we move down the group.