Q.Which of the following lattices has the highest packing efficiency

Square close packing is a way of arranging spheres in a two-dimensional layer where each sphere touches 4 neighbours — placed directly above, below, left and right — so the centres form a square pattern (also called AAAA type since rows align).

Key facts:

• Coordination number = 4 in the layer.
• The empty spaces (voids) between spheres are square.
• It is less efficient than hexagonal close packing (2D), where each sphere touches 6 neighbours and voids are triangular. …