MCQ
Which pair of atomic numbers represents $s$-block elements
- A$7, 15$
- B$6, 12$
- C$9, 17$
- ✓$3, 12$
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(Given : Energy of the electron in the first shell of the hydrogen atom is $-2.2 \times 10^{-18} \,J$; $h =6.63 \times 10^{-34}\, Js$ and $c =3 \times 10^{8} \,ms ^{-1}$ )

