Free Chemistry in Daily Life MCQs with Answers

251. Which of the following is the hardest substance?

• A. Copper
• B. Diamond
• C. Iron
• D. Silicon

Explanation: Diamond is the hardest naturally occurring substance because its carbon atoms are locked in a strong three-dimensional covalent network. Copper, iron, and silicon are much softer in the usual hardness comparison.

252. According to many, including the Guinness Book of World Record,________is the world's rarest mineral?

• A. Painite
• B. Benitoite
• C. Jadeite
• D. Taaffeite

Explanation: Painite was long listed by Guinness and other references as the world's rarest mineral because only a few specimens were known. Although later discoveries changed its absolute rarity, painite is the conventional answer to this textbook question.

253. Density of Milk is________?

• A. 1.024 g/cm3
• B. 1.034 g/cm3
• C. 1.044 g/cm3
• D. 1.054 g/cm3

Explanation: Milk is slightly denser than water because it contains dissolved proteins, sugars and minerals, with typical density around 1.03 to 1.04 g/cm³. Thus 1.034 g/cm³ is the closest listed value.

254. Chemical Name of Dry Ice?

• A. Solid Carbon Dioxide
• B. Calcium Carbon
• C. A&B
• D. Sodium Oxide

Explanation: Dry ice is carbon dioxide in its solid state, written as CO₂(s). It changes directly into gas by sublimation rather than melting at ordinary pressure.

255. Boiling of an egg is a change which is__________?

• A. Physical
• B. Chemical
• C. Physiological
• D. Morphological

Explanation: Boiling an egg is a chemical change because heat permanently denatures and coagulates its proteins, especially albumin. The cooked egg cannot be changed back into a raw egg by cooling.

256. The major ingredient of leather is__________________?

• A. Collagen
• B. Polymer
• C. Nucleic acid
• D. None of these

Explanation: Leather is mainly made of collagen, a strong fibrous protein present in animal skin. Tanning stabilizes these collagen fibres and makes the skin durable and resistant to decay.

257. Glass is made of the mixture of______________?

• A. Quartz and Mica
• B. Sand and Salt
• C. Sand and Silicates
• D. None of these

Explanation: Ordinary glass is produced mainly from silica-rich sand along with alkaline substances such as sodium carbonate and other silicates. Thus sand and silicates is the closest option, although the wording simplifies the full mixture.

258. Rusting of Iron involves_______________?

• A. Reduction
• B. Oxidation
• C. Decomposition
• D. Displacement

Explanation: Rusting is an oxidation process in which iron reacts with oxygen and moisture to form hydrated iron(III) oxide. Although reduction occurs in the accompanying electrochemical reaction, iron itself is oxidized.

259. The horizontal rows of the periodic table are called ______?

• A. Groups
• B. Periods
• C. Sets
• D. Matrices

Explanation: The horizontal rows of the periodic table are called periods, and the vertical columns are called groups. Elements in the same period have the same number of occupied electron shells.

260. Which metallic element is liquid at room temperature?

• A. Zinc
• B. Nickel
• C. Lead
• D. Mercury

Explanation: Mercury is a metal that remains liquid at ordinary room temperature because its melting point is about −39°C. Zinc, nickel, and lead are solid at room temperature.