Free Chemistry in Daily Life MCQs with Answers

271. "Rancidity produced in butter can be decreased by adding quinoline to the butter". This statements shows that _______________?

• A. Nothing is impossible
• B. Quinoline is an inhibitor
• C. Quinoline is a catalyst
• D. Quinoline is an activator

Explanation: Rancidity is mainly oxidation of fats, so a substance that slows this reaction acts as an inhibitor, often called an antioxidant. A catalyst would speed a reaction rather than reduce rancidity.

272. In the Composition of the earth, Aluminum is _______________?

• A. 27.5%
• B. 20.3%
• C. 14.5%
• D. 8.23%

Explanation: Aluminium makes up about 8.2% of the Earth's crust by mass, making it the third most abundant crustal element after oxygen and silicon. The question should technically specify the crust rather than the whole Earth.

273. A substance which increases the efficiency of a catalyst is termed as:

• A. Promoter
• B. Activator
• C. Retarder
• D. Super catalyst

Explanation: A promoter increases a catalyst’s activity or efficiency without itself functioning as the main catalyst. A retarder has the opposite effect by slowing the reaction or reducing catalytic activity.

274. One of the following ways of expressing the concentration of a solution does not depend on temperature. It is__________?

• A. Molarity
• B. Molality
• C. Normality
• D. Formality

Explanation: Molality is moles of solute per kilogram of solvent, and mass does not change appreciably with temperature. Molarity, normality, and formality use solution volume, which expands or contracts with temperature.

275. "Each electron in an atom must have its own unique set of quantum numbers" is a statement of_______________?

• A. Aufbau principle
• B. Pauli exclusion principle
• C. Hund's rule
• D. Periodic law

Explanation: The Pauli exclusion principle states that no two electrons in an atom can have the same four quantum numbers. Aufbau describes filling order, while Hund’s rule describes how electrons occupy equal-energy orbitals.

276. Second ionization energy:

• A. is always less than first ionization energy
• B. is always greater than first ionization energy
• C. is equal to the first ionization energy
• D. may be greater or less than the first ionization energy depending on the nature of the element

Explanation: After the first electron is removed, the atom becomes positively charged, so the remaining electrons are held more strongly by the nucleus. Therefore, the second ionization energy is always greater than the first.

277. Nuclear radiation is emitted by those elements whose:

• A. molecules are stable
• B. molecules are unstable
• C. nuclei are stable
• D. nuclei are unstable

Explanation: Nuclear radiation is released when an unstable atomic nucleus changes into a more stable state. Molecular stability does not determine whether an element is radioactive.

278. Color of the glow produced in the discharge tube:

• A. depends on the pressure in the discharge tube
• B. depends on the metal used as cathode
• C. depends on the gas used in the discharge tube
• D. does not depend on the nature of the gas used in the discharge tube

Explanation: In a discharge tube, excited atoms or molecules emit their characteristic colours as they return to lower energy levels. Thus, the gas used, rather than the cathode metal, mainly determines the glow colour.

279. Covalent network crystals have_____________?

• A. higher melting point then molecular crystals
• B. lower melting point then molecular crystals
• C. discrete molecules linked by Van der waals forces
• D. hydrogen bonding

Explanation: Covalent network crystals contain atoms joined throughout a strong covalent framework, so breaking the structure requires much more energy than separating molecular crystals. They consequently have higher melting points than molecular crystals.

280. The increasing vapor pressure caused by heating a liquid is due to___________?

• A. increase inter-molecular interactions
• B. increasing potential energy of molecules
• C. increasing kinetic energy of molecules
• D. decreasing surface tension

Explanation: Heating gives liquid molecules greater kinetic energy, allowing more of them to escape from the surface into the vapour phase. This increases the equilibrium vapour pressure.