Explanation

• Atoms with the same atomic number but different mass numbers are called isotopes.
• Atomic number depends on the number of protons.
• Mass number depends on protons + neutrons.
• So, difference in mass number comes from variation in neutrons.
• Isotopes have similar chemical properties but different physical properties.

Last verified on 08-05-2026

Explanation

• Natural gas contains about 80% to 95% methane.
• It is a hydrocarbon fuel.
• It is the chief (major) component of natural gas.
• It is also a greenhouse gas.
• Chemical formula: CH₄
• It is a clean-burning fuel used in daily life.

Last verified on 07-05-2026

Explanation

• Isobars are atoms of different elements.
• They have same mass number but different atomic number.
• They show different chemical properties but same nuclear mass.
• Example: Argon-40 and Calcium-40 both have mass number 40 but different atomic numbers.

Last verified on 07-05-2026

Explanation

• The atomic number of an element is equal to the number of protons present in its nucleus.
• If the number of protons increases, the element itself changes because its atomic number changes.
• Protons are positively charged particles.
• The mass number is calculated by adding protons and neutrons.

Last verified on 07-05-2026

Explanation

• Isotopes of an element have the same number of protons and electrons.
• Because of this, their electronic configuration remains the same.
• Hence, their chemical behavior does not change, even though mass differs.

Last verified on 06-05-2026

Explanation

• An electron carries a negative charge.
• When an atom loses one electron, it loses negative charge.
• As a result, the atom becomes positively charged (cation).
• Atoms become ions to achieve stability (octet rule).

Last verified on 06-05-2026

Explanation

• Atoms of the same element always have the same atomic number.
• Sometimes, they differ in mass due to neutrons.
• Such atoms have identical chemical behavior.
• They differ only in mass number, not in properties.
• These are called isotopes.

Additional information:

• Radioactive isotopes are used in medicine and industry.
• Carbon-14 is used for age determination (carbon dating).

Last verified on 04-05-2026

Explanation

• Atomic number is a fundamental property of an element.
• It defines the identity of an element in the periodic table.
• It is based on particles present in the nucleus.
• Specifically, it depends on the number of protons.
• Each element has a unique atomic number.

Last verified on 04-05-2026

Explanation

• Brass is an alloy mainly made of copper and zinc.
• In air, there are various gases including oxygen, carbon dioxide, moisture, and traces of hydrogen sulphide (H₂S).
• The gas responsible for discoloration of brass is hydrogen sulphide.
• Hydrogen sulphide reacts with copper present in brass to form copper sulphide.
• This copper sulphide forms a dark layer, causing brass to lose its shine and colour (tarnishing).

Last updated question by NS on 2 MAY 2026

Explanation

• Tetraethyl lead is primarily used as an antiknock agent
• Octane booster in gasoline and aviation fuel.
•  It prevents "knocking" (premature ignition of petrol vapors) in motors.
• Highly toxic and easily absorbed through the skin, lungs, and gastrointestinal tract

Last updated question by NS on 2 MAY 2026