Which of the following is not a possible sublevel? 1p 2s 3d 4f

Answer is: 1p.

First energy level only have one sublevel 1s.

Second energy level has 2s and 2p, third has 3s, 3p and 3d and fourth has 4s, 4p, 4s and 4f.

Aufbau principle is a scheme used to reproduce the electron configurations of the ground states of atoms by successively filling subshells (orbitals) with electrons in a specific order.

Filling subshells in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.