All Free Everyday Science MCQs with Answers

331. Oxidation is a chemical reaction involving the __________?

• A. Gain of Electrons
• B. Loss of Electrons
• C. Gain of Protons
• D. Loss of Protons

Explanation: In modern redox terminology, oxidation means loss of electrons, while reduction means gain of electrons. The mnemonic OIL, Oxidation Is Loss, helps distinguish the two.

332. In a very low temperature which from the following will freeze at last?

• A. River water
• B. Canal water
• C. Sea water
• D. Water in a lake

Explanation: Sea water freezes last because dissolved salts lower its freezing point below that of fresh water. River, canal and lake water generally contain much less dissolved salt.

333. During winter in cold countries, the __________ is mixed to melt the ice on the icy roads.

• A. Salt
• B. Chlorine
• C. Carbon dioxide
• D. Water

Explanation: Salt lowers the freezing point of water, so ice melts even when the road temperature is below 0°C. Chlorine and carbon dioxide do not serve this ordinary road-deicing purpose.

334. The most densest substance on the Earth is __________.

• A. Platinum
• B. Copper
• C. Steel
• D. Osmium

Explanation: Osmium has the greatest density among the commonly recognized elements, about 22.6 g/cm³. Platinum, copper and steel are substantially less dense.

335. The gas used in a refrigerator to cool water is___________?

• A. Nitrogen
• B. Carbon dioxide
• C. Methane
• D. Tetrafluoroethane

Explanation: Tetrafluoroethane is a refrigerant used in many modern refrigerators and air-conditioning systems because it absorbs heat during evaporation. Nitrogen, carbon dioxide and methane are not the usual answer for this appliance.

336. The density of water is __________?

• A. 1 g/cm3
• B. 1.5 g/cm3
• C. 2 g/cm3
• D. none of these

Explanation: Water has a density of approximately 1 g/cm³, or 1000 kg/m³, at about 4°C. Its density changes slightly with temperature, but 1 g/cm³ is the standard value used in basic science.

337. Identify the monoatomic molecule among the following?

• A. Helium
• B. Ozone
• C. Hydrogen
• D. Nitrogen

Explanation: Helium exists naturally as individual atoms, so it is monatomic. Hydrogen and nitrogen are diatomic molecules, while ozone contains three oxygen atoms per molecule.

338. The maximum number of electrons can be filled in the first shell of an atom are _____.

• A. 2 electrons
• B. 8 electrons
• C. 18 electrons
• D. 4 electrons

Explanation: The first electron shell has principal energy level n = 1, so its capacity is 2n² = 2 electrons. The capacities 8 and 18 apply to higher shells, not the first shell.

339. What pigment is responsible for the red color inside a watermelon?

• A. Chlorophyll
• B. Beta-carotene
• C. Lycopene
• D. Anthocyanin

Explanation: Lycopene is the red carotenoid pigment responsible for the red flesh of many watermelons and tomatoes. Chlorophyll is green, beta-carotene is orange, and anthocyanins produce red, purple or blue colours in many other plants.

340. Which of the following is used as a lubricant?

• A. Graphite
• B. Silica
• C. Iron oxide
• D. Diamond

Explanation: Graphite has a layered structure, allowing its sheets to slide over one another and reduce friction. Diamond is also carbon, but its rigid crystal structure makes it an abrasive rather than a common lubricant.