1. Identify the elements from their electronic configurations

Given:

• $A: 1s^2 2s^2 2p^3$
  Total electrons $= 7 \Rightarrow A = \text{N}$
• $B: 1s^2 2s^2 2p^4$
  Total electrons $= 8 \Rightarrow B = \text{O}$
• $C: 1s^2 2s^2 2p^5$
  Total electrons $= 9 \Rightarrow C = \text{F}$
• $D: 1s^2 2s^2 2p^2$
  Total electrons $= 6 \Rightarrow D = \text{C}$

So we have: $A=\mathrm{N},\quad B=\mathrm{O},\quad C=\mathrm{F},\quad D=\mathrm{C}$

2. Recall the trend of electronegativity across Period 2

Across a period, electronegativity generally increases from left to right due to increasing effective nuclear charge.

For the elements involved: $\mathrm{C} < \mathrm{N} < \mathrm{O} < \mathrm{F}$

In terms of $A,B,C,D$:

• $D = \mathrm{C}$
• $A = \mathrm{N}$
• $B = \mathrm{O}$
• $C = \mathrm{F}$

Therefore, the increasing order is: $D < A < B < C$

3. Match with the options

• Option A: $D < A < B < C$ ✅
• Option B: $A < B < C < D$ ❌
• Option C: $A < C < B < D$ ❌
• Option D: $A < D < B < C$ ❌

Hence, the correct option is A.