Which of the following factors is primarily responsible for the smaller atomic radius of
gallium (Ga) compared to aluminium (Al)?

a. Poor screening effect of 3d 

b. Increase in nuclear charge

c. Presence of higher orbitals

d. Higher atomic number

Choose the correct option
1. (a, b)
2. (b, c)
3. (c, d)
4. (a, d)