Group 13 Elements

Answer (c) Gallium

aqueous acid ions give a complex ion in which ion form six coordinate covalent bonds with six molecules. Hence, it shows hybridisation. (Due to availability of vacant -orbitals.)

Four electron pairs denoted by molecules

Step 1: Understanding the Concept:
The atomic (or metallic/covalent) radius of elements follows specific periodic trends:
1. It decreases across a period from left to right due to increasing effective nuclear charge, which pulls the electron cloud closer to the nucleus.
2. It increases down a group from top to bottom due to the addition of new principal electron shells, which outweighs the increase in nuclear charge.

Step 2: Key Formula or Approach:
Locate the given elements in the periodic table to compare their radii based on periods and groups.

Step 3: Detailed Explanation:
Let's place the elements in their respective periods and groups:
- Period 2: Li (Group 1), Be (Group 2), B (Group 13)
- Period 3: Mg (Group 2), Al (Group 13)
First, apply the trend across Period 2:

Next, apply the trend across Period 3:

Now, compare elements down the groups (Period 3 elements are generally larger than Period 2 elements of the same or nearby groups):
- Mg is below Be, so Mg Be.
- Al is below B, so Al B.
Comparing Li and Mg: This is a diagonal relationship, but generally, Group 1 elements are very large. The standard metallic radius of Mg ( pm) is slightly larger than Li ( pm).
Comparing Li and Al: Li ( pm) is larger than Al ( pm).
Combining these observations with standard values:
Mg (160 pm) Li (152 pm) Al (143 pm) Be (112 pm) B (85 pm)
Thus, the decreasing order is Mg Li Al Be B.

Step 4: Final Answer:
The correct order is Mg Li Al Be B.