The correct order of first ionization enthalpy values of the following elements is: (A) O (B) N (C) Be (D) F (E) B. Choose the correct answer from the options given below : 

We need to find the correct order of first ionization enthalpy for the elements:

(A) O (Z=8), (B) N (Z=7), (C) Be (Z=4), (D) F (Z=9), (E) B (Z=5)

Electronic configurations:

(E) B: $$1s^2\,2s^2\,2p^1$$

(C) Be: $$1s^2\,2s^2$$

(A) O: $$1s^2\,2s^2\,2p^4$$

(B) N: $$1s^2\,2s^2\,2p^3$$

(D) F: $$1s^2\,2s^2\,2p^5$$

Key points about ionization enthalpy trends:

1. General trend: IE increases across a period (left to right) due to increasing nuclear charge.

2. Anomaly 1: Be ($$2s^2$$, fully filled) has higher IE than B ($$2s^2\,2p^1$$) because removing a $$2p$$ electron is easier than removing a $$2s$$ electron.

3. Anomaly 2: N ($$2p^3$$, half-filled) has higher IE than O ($$2p^4$$) because the half-filled $$2p$$ subshell has extra exchange stability.

Standard IE$$_1$$ values (kJ/mol):

B: 801 < Be: 900 < O: 1314 < N: 1402 < F: 1681

In terms of labels: E < C < A < B < D

The correct answer is Option A: E < C < A < B < D.