Which of the Following Statements Is/are CORRECT for an Oxygen

Multiple Choice

Which of the following statements is/are CORRECT for an oxygen atom?
1) The effective nuclear charge felt by a 2s electron is greater than that felt by a 1s electron.
2) The effective nuclear charges felt by 2s and 2p electrons are identical.
3) The effective nuclear charge felt by a 2p electron is less than that felt by a 2s electron.

A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
E) 1,2,and 3