d. Both are points

Explanation: Coulomb's law applies specifically to point charges, which are idealized as having no size. It describes the force between two point charges. While it can be extended to spherical charges (considered as point charges at their centers), it is most accurate when both charges are points.

d. High resistance, low melting point

Explanation:

A fuse wire is designed to protect electrical circuits by melting and breaking the circuit when current exceeds a safe limit. It needs:

• High resistance: To generate enough heat when excess current flows.
• Low melting point: So it can melt quickly to stop the current and protect the circuit.

c. Two protons, two neutrons

Explanation:

An α-particle (alpha particle) is essentially a helium nucleus, which consists of:

• 2 protons
• 2 neutrons

It has no electrons, making it positively charged. Therefore, the correct composition is two protons and two neutrons.

d. Radioactivity

Explanation: Periodic properties are characteristics of elements that show a trend across the periodic table, such as density, melting point, and boiling point. Radioactivity, however, is not a periodic property because it does not follow a consistent trend and varies widely among elements, particularly among heavy elements.

b. Calcium oxide

Explanation: Calcium oxide (CaO) is an ionic compound that exists as a lattice structure rather than as discrete molecules. In contrast, hydrogen chloride (HCl), methane (CH₄), and ammonia (NH₃) are all molecular compounds composed of individual molecules.

d. the concentration of CuSO₄ in the solution remains unchanged

Explanation: The correct statement is: the mass of the cathode increases and the mass of the anode decreases. The concentration of CuSO4 in the solution remains unchanged.

a. Violet

Explanation:

When H₂S gas is passed through an alkaline aqueous solution of sodium nitroprusside, a violet colour is produced. This occurs due to the formation of a complex between sulfide ions and the nitroprusside.

b. Fe₂O₃

Explanation:

The formula for red haematite, an ore of iron, is Fe₂O₃, which indicates it contains two iron atoms for every three oxygen atoms.

d. CH₃COOH

Explanation:

When aqueous NaHCO₃ (sodium bicarbonate) reacts with acetic acid (CH₃COOH), it produces carbon dioxide (CO₂) gas. The reaction is:

CH₃​COOH + NaHCO₃ → CH₃COONa + H₂O+CO₂

Methane is the fuel gas harvested from coal beds, often referred to as coal-bed methane (CBM).

OR

For the second question: The gas in air that contributes to global warming is Carbon dioxide (CO₂).

An energy source that can be used for sustainable development is solar energy.

False

Explanation:

Even at a fixed temperature and pressure, gas molecules in a closed vessel do not all move at the same speed.