# NCERT Class-9 Science Solutions: Chapter 4-Structure of the Atom Part 7 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 35:

An element X has a mass number 4 and atomic number 2. Write the valency of this element?

Valency is zero as K shell is completely filled.

Question 36:

Why do Helium, Neon and Argon have a zero valency?

Helium has two electrons in its only energy shell, while Argon and Neon have 8 electrons in their valence shells. As these have maximum number of electrons in their valence shells, they do not have any tendency to combine with other elements. Hence, they have a valency equal to zero.

Question 37:

The ratio of the radii of hydrogen atom and its nucleus is . Assuming the atom and the nucleus to be spherical, (i) what will be the ratio of their sizes? (ii) If atom is represented by planet earth , estimate the size of the nucleus.

Question 38:

Enlist the conclusions drawn by Rutherford from his α-ray scattering experiment.

Rutherford concluded from the scattering experiment that -

1. Most of the space inside the atom is empty because most of the passed through the gold foil without getting deflected.
2. Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.
3. A very small fraction of were deflected by , indicating that all the positive charges and mass of the gold atom were concentrated in a very small volume within the atom.

From the data he also calculated that the radius of the nucleus is about times less than the radius of the atom.

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