What is the coordination number in a square close packed structure in two dimensions?

The correct option is A $4$
$\text{Coordination number in square close packed structure}$

• In square closed packing in $2-D$ ($AAAA$ type), spheres in the second row will be placed in such a way that they are touching each sphere of the first row and exactly above the sphere of the first row.
• In a square close packed structure $(2-D)$, any particle is in contact with four of its neighbors. Therefore, the two-dimensional coordination number of a molecule in a square close packed structure is $4$.