Answer:
1s2 2s2 2p6 3s2 3p4
Step-by-step explanation:
For ground state atoms you need to fill the orbitals in order.
Orbital s has max 2 electrons
Orbital p has max 6 electrons
Level 1 only has s orbital
Level 2 has s and p orbitals
Level 3 has s, p and d orbitals
You fill them in order until you reach 16 electrons:
1s2 2s2 2p6 3s2 3p4