NCERT Class 9 Science — Chapter 4: Structure of the atom

mcqeasy

Which of the following elements has a valency of zero?

Official previous-year question

Verified 1 Aug 2026.

Options

ANeon
BSilicon
CNitrogen
DHydrogen

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Solution

The correct option is

Neon

Explanation

Valency is defined as the combining capacity of an element, which is determined by the number of electrons present in the outermost shell (valence electrons). Elements react to achieve a stable electronic configuration, typically an octet (8 electrons) in the outermost shell.

The valency of the given elements is analyzed as follows:

Hydrogen (Atomic No. 1): It has 1 electron in its outermost shell ($K$ shell). It needs 1 more electron to complete its duplet (stable configuration like Helium). Hence, its valency is 1.
Nitrogen (Atomic No. 7): Its electronic configuration is 2, 5. It has 5 valence electrons and requires 3 more to complete its octet. Hence, its valency is 3.
Neon (Atomic No. 10): Its electronic configuration is 2, 8. The outermost shell is completely filled with 8 electrons (stable octet). Consequently, it has no tendency to lose, gain, or share electrons under normal conditions. Hence, its valency is 0.
Silicon (Atomic No. 14): Its electronic configuration is 2, 8, 4. It has 4 valence electrons and typically shares them to achieve stability. Hence, its valency is 4.

Key Takeaway: Noble gases (Group 18 elements like Helium, Neon, Argon) possess a stable, fully filled outermost shell, resulting in a zero valency as they are chemically inert.

Your note

More from Chapter 4: Structure of the atom

Which sub-atomic particle was identified by J. Chadwick in 1932?

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With reference to Neils Bohr’s model of the atom, consider the following statements: 1. Only certain special orbits known as discrete orbits of electrons are allowed inside the atom. 2. Electrons radiate energy continuously while revolving in discrete orbits. 3. These discrete orbits are called energy levels. Which of the statements given above is/are correct?

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Consider the following statements regarding the discovery and properties of neutrons: 1. They were discovered by J.J. Thomson in 1897. 2. They are present in the nucleus of all atoms including hydrogen. 3. A neutron has no charge and a mass nearly equal to that of a proton. Which of the statements given above is/are correct?

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With reference to 'Valency', consider the following statements: 1. It is the combining capacity of the atoms of elements. 2. Atoms react to achieve a duplet in the outermost shell in all cases. 3. If the outermost shell has 8 electrons, the valency is 8. Which of the statements given above is/are correct?

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With reference to the definition of an element, consider the following statements: 1. Elements are defined by the number of protons they possess. 2. Atoms of a given element can have different numbers of protons. 3. The atomic number is characteristic of a particular element.

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Keep practising Chapter 4: Structure of the atom

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The correct option is

Neon

Explanation

The valency of the given elements is analyzed as follows:

Hydrogen (Atomic No. 1): It has 1 electron in its outermost shell ($K$ shell). It needs 1 more electron to complete its duplet (stable configuration like Helium). Hence, its valency is 1.
Nitrogen (Atomic No. 7): Its electronic configuration is 2, 5. It has 5 valence electrons and requires 3 more to complete its octet. Hence, its valency is 3.
Neon (Atomic No. 10): Its electronic configuration is 2, 8. The outermost shell is completely filled with 8 electrons (stable octet). Consequently, it has no tendency to lose, gain, or share electrons under normal conditions. Hence, its valency is 0.
Silicon (Atomic No. 14): Its electronic configuration is 2, 8, 4. It has 4 valence electrons and typically shares them to achieve stability. Hence, its valency is 4.

Key Takeaway: Noble gases (Group 18 elements like Helium, Neon, Argon) possess a stable, fully filled outermost shell, resulting in a zero valency as they are chemically inert.