Explanation

• Allotropy is the ability of an element to exist in two or more different structural forms in the same physical state.
• Oxygen exists as dioxygen (O₂) and ozone (O₃).
• Sulphur exists in different allotropic forms, mainly rhombic and monoclinic sulphur.

Last verified on 01-11-2026

Explanation

• Metallic bonding consists of positive metal ions surrounded by a sea of delocalized, freely moving electrons.
• These mobile electrons allow metals to conduct electricity and heat efficiently.
• The attraction between positive metal ions and delocalized electrons holds the metallic structure together.

Last verified on 01-11-2026

Explanation

• Electron affinity measures the energy change when a neutral gaseous atom gains an electron to form a negative ion.
• Elements with a greater tendency to accept electrons generally have a higher electron affinity.

Additional information:

• Electronegativity describes an atom's ability to attract shared electrons in a chemical bond.

Last verified on 01-11-2026

Explanation

• Fluorine is more reactive than chlorine and can displace chlorine from sodium chloride.
• The liberated chlorine gas has a characteristic greenish-yellow colour.

Last verified on 01-11-2026

Explanation

• Alkaline earth metals lose 2 electrons to form M2+ ions.
• Halogens gain electrons to form X- ions.
• Both oxidation and reduction occur, so it is a redox reaction.

Last verified on 01-11-2026

Explanation

Potassium is more reactive than Sodium in reactivity series.

So potassium displaces sodium from NaCl:

2K + 2NaCl -> 2KCl + 2Na

And in water it also reacts:

2K + 2H2O -> 2KOH + H2

So it is a Displacement reaction.

Last verified on 01-11-2026

Explanation

• The reactivity of alkali metals increases down Group 1 of the periodic table.
• Potassium reacts more vigorously with cold water than lithium and sodium.
• The reaction produces potassium hydroxide and hydrogen gas, releasing heat that may ignite the hydrogen.

Last verified on 01-11-2026

Explanation

• 6.02 × 10²³ is Avogadro's number, which represents one mole of particles.
• One mole of water contains 6.02 × 10²³ water molecules and has a mass of approximately 18 grams.

Last verified on 01-11-2026

Explanation

• One gram molecular mass means molecular mass expressed in grams.
• One mole of water H2O has mass 18 grams, equal to its molecular mass in grams.
• One mole of water contains 6.022 x 10^23 molecules.

Last verified on 01-11-2026

Explanation

• An empirical formula represents the simplest whole-number ratio of atoms of each element in a compound.
• For example, the molecular formula of glucose is C₆H₁₂O₆, while its empirical formula is CH₂O.

Additional information:

• The molecular formula shows the actual number of atoms in a molecule.
• Empirical formula shows their simplest ratio.

Last verified on 01-11-2026