Concept:
The isometric (cubic) crystal system is the most symmetric of all the crystal systems. Its highest symmetry class shows the maximum number of symmetry elements.
Step 1:
The holosymmetric (normal) class of the isometric system contains a centre of symmetry, several planes of symmetry, and many axes of symmetry.
Step 2:
Counting the symmetry elements in the isometric system, the total degree of symmetry comes to 23, which is the largest among the crystal systems.
Answer: Option (1) — 23.