18. Possible values of the principal quantum number n for an electron in an atom are: (A) 0 and 1 (B) 2,4,6,... (C) 0,1,2,... (D) 1,3,5,... (E) 1,2,3,...

10. In an oscillating series RLC circuit with R = 50 Ω, L = 20 mH and C = 2.0 μF, the maximum charge is stored on the capacitor at t = 0. Find the time required for the charge on the capacitor falling to 37% of its initial value. (A) 1. × 10⁻⁴ s (B) 2. × 10⁻⁴ s (C) 4. × 10⁻⁴ s (D) 6. × 10⁻⁴ s (E) 8. × 10⁻⁴ s