Cross word puzzle

Clues:

Down:

1. Helium Nuclei (Particle)

2. Positive Charge mass at the core of the atom

3. An atom whose valency is zero

4. One or two electrons in the outermost shell of atoms of elements are called as ______________ electrons.

5. ¹⁴₆C is used for carbon dating

6. Discovery of neutron

Across:

1. Electrons present in the outermost shell

2. This pair of atoms ⁴⁰₂₀Ca, ⁴⁰₁₈Al are ____

3. An atom that does not have neutron

4. Scattering of α particles in the gold foil experiment