Explanation

NO₂ (Nitrogen dioxide) is a covalent compound, made of nonmetals (nitrogen and oxygen) sharing electrons.

The others like (NH₄)₂CO₃, HNO₃, and AgCl involve ionic bonding either fully or in part (e.g., NH₄⁺ acts ionically).

Explanation

Dative bond: This is a type of covalent bond where one atom donates both electrons to the bond, forming a coordinate covalent bond.

In this case, NH₃ (ammonia) (with a lone pair of electrons) acts as the electron donor, and BF₃ (boron trifluoride) (electron deficient) acts as the electron acceptor.

Explanation

John Dalton proposed the Atomic Theory in the early 1800s, stating that all elements are made of indivisible atoms.

He described atoms as indestructible and identical for each element, laying the foundation of modern chemistry.

Explanation

A reaction in which heat is absorbed is called an endothermic reaction.

These reactions lower the temperature of their surrounding area, thereby creating a cooling effect.

Explanation

• When blue litmus paper is dipped in an acid, it turns red.
• This is because the acid changes the color of the litmus paper from blue to red.

Note: When red litmus paper is dipped in a base, it turns blue.

Explanation

An exothermic reaction releases heat to the surroundings.

Examples include combustion and neutralization reactions.

An endothermic reaction absorbs heat from the surroundings.

Examples include photosynthesis and melting of ice.

Explanation

When water acts as the solvent in dissolving a substance, the process is called hydration.

It involves the attachment of water molecules to the ions or molecules of the solute.

Explanation

Explanation

A neutral sodium atom (Na) has 11 electrons.

Na⁺ loses 1 electron, so it has 10 electrons.

Explanation

Calcium Sulphate hemihydrate (CaSO₄·½H₂O) is commonly called Plaster of Paris.

It is used in casts, molds, and construction materials.