Explanation

• Carbon is a tetravalent element.
• It forms 4 covalent bonds in most compounds.
• In C₂H₆O (ethanol or dimethyl ether), carbon still makes 4 bonds.
• Valency is based on bonding capacity, not charge here.
• So, carbon’s valency remains 4.

Last verified on 12-04-2026

Explanation

Use the first law of thermodynamics: ΔU = Q + W

Sign convention:  

Heat added _to_ system: Q = +20 kJ

Work done _on_ system: W = +60 kJ

ΔU = 20 + 60 = 80 kJ

Last verified on 12-04-2026

Explanation

• When two or more substances are physically combined, they form a mixture.
• In a mixture, components retain their properties.
• They can be separated by physical methods like filtration or evaporation.
• No chemical bonding is involved.
• Therefore, such elements form a mixture.

Last verified on 12-04-2026

Explanation

• Group 17 elements are called halogens.
• They are highly reactive non-metals.
• These elements readily gain one electron.
• Chlorine is a member of Group 17.

Last verified on 12-04-2026

Explanation

• A mole is a unit used in chemistry.
• It represents a very large number of particles.
• This number is called Avogadro’s number.
• 1 mole contains 6.02 × 10²³ particles.
• These particles can be atoms, molecules, or ions.

Last verified on 12-04-2026

Explanation

• A new predator increases predation pressure on prey.
• This leads to a decrease in prey population.
• More prey get hunted and fewer survive.
• Ecosystem balance may temporarily change.
• So, prey population is most directly affected.

Last verified on 12-04-2026

Explanation

• Pepsin is a digestive enzyme in the stomach.
• It works best in strong acidic conditions (low pH).
• This means enzymes have an optimum pH range.
• Outside this range, activity decreases.
• So, it does not work equally at all pH levels.

Last verified on 12-04-2026

Explanation

• Adaptation helps organisms survive in their environment.
• It improves their ability to cope with changes.
• Adapted organisms reproduce more successfully.
• This increases survival chances of the species.
• So, adaptation enhances both survival and reproduction.

Last verified on 12-04-2026

Explanation

• A cell with one cytoplasm and two nuclei indicates division of nucleus but not cytoplasm.
• This means karyokinesis occurred but cytokinesis did not.
• The cytoplasm failed to divide after nuclear division.
• So the correct situation is cytokinesis failure.
• This results in multinucleated cells.

Last verified on 12-04-2026

Explanation

• Gastric juice helps in digestion of food in the stomach.
• It contains acid (HCl) and enzymes like pepsin.
• If its production stops, food cannot be properly digested.
• The immediate effect will be failure of digestion.
• Nutrient breakdown in stomach becomes impossible.

Last verified on 12-04-2026