An atom with 3 protons and 4 neutrons will have a valency of :

Question

Accepted Answer

An atom with 3 protons is an atom of lithium, as the atomic number, which is the number of protons, determines the element. Lithium has an atomic number of 3. The electronic configuration of lithium is 1s² 2s¹. This means that in its outermost shell, lithium has one electron.

Valency is determined by the number of electrons in the outermost shell of an atom. It is the ability of an atom to bond with other atoms, which is often achieved by losing, gaining, or sharing electrons to achieve a stable electronic configuration, typically that of the nearest noble gas.

1. **Explanation for Option 2 (Correct Answer):**  
   Lithium has one electron in its outermost shell (2s¹). To achieve a stable configuration similar to the nearest noble gas (helium, in this case), lithium tends to lose one electron. Therefore, the valency of lithium is 1, as it can form bonds by losing one electron.

2. **Explanation for why other options are incorrect:**

- **Option 1 (7):**  
     A valency of 7 would imply that the atom needs to gain or share 7 electrons to achieve a stable configuration. This is not possible for lithium, as it only has one electron in its outermost shell and tends to lose it rather than gain additional electrons.

- **Option 3 (3):**  
     A valency of 3 would suggest that the atom needs to gain or share 3 electrons. However, lithium only has one electron in its outermost shell and achieves stability by losing this electron, not by gaining more.

- **Option 4 (4):**  
     A valency of 4 would imply that the atom can form bonds by gaining, losing, or sharing 4 electrons. Lithium does not have 4 electrons in its outermost shell; it only has one, which it loses to achieve a stable configuration.

In conclusion, the valency of an atom with 3 protons and 4 neutrons, which is lithium, is 1. This is because lithium loses one electron to achieve a stable electronic configuration, supporting Option 2 as the correct answer.