What will be the valency of an atom with 3 protons and 4 neutrons? 

1

The correct answer is option 3. 1.

To determine the valency of an atom based on its protons and neutrons, we need to first identify the atomic number of the atom. The atomic number is equal to the number of protons in the nucleus of the atom.

Given that the atom has 3 protons, its atomic number is 3. This means the atom is lithium (Li), as lithium has an atomic number of 3.

The valency of an atom is determined by its ability to gain or lose electrons to achieve a stable electron configuration. For Group 1 elements like lithium, the valency is typically +1, as these elements tend to lose one electron to achieve a stable electron configuration.

So, the valency of the atom with 3 protons and 4 neutrons (which is lithium) would be +1