Answer:
(a) Rb
(b) Ge
(c) Ar

Explanation:
(a) Rb
Atomic number = 37
The electronic configuration is -
(b) Ge
Atomic number = 32
The electronic configuration is -
(c) Ar
Atomic number- 18
The electronic configuration is -

Microscopes, balances,scales
The answer to this would be d. Precipitation patterns .