Empty space present in FCC is

The correct answer is Option (2) → 26%

In a face-centred cubic (ccp) lattice there are 4 atoms per unit cell and the atoms touch along the face diagonal, so a√2 = 4r, that is a = 2√2 r.

    Packing efficiency = (4 × 4/3 πr³) / (2√2 r)³ × 100 = (16/3 πr³) / (16√2 r³) × 100 = 74%

So 74% of the volume is filled by the spheres and the empty space = 100 − 74 = 26%.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Close Packed Structures – “… This pattern of layers is often written as ABCABC … This structure is called cubic close packed (ccp) or face-centred cubic (fcc) structure. Metals such as copper and silver crystallise in this structure. Both these types of close packing are highly efficient and 74% space in the crystal is filled. In either of them, each sphere is in contact with twelve spheres. Thus, the coordination number is 12 in either of these two structures.”