壳 has two pronunciations: ké (colloquial, used in daily speech like 蛋壳, 贝壳) and qiào (more formal/literary, used in compounds like 地壳 dìqiào 'earth's crust'). In everyday use, ké is far more common.
memory
Think of cracking open a nut — 壳 is the outer covering you break through to get to the good stuff inside.
