All Free Everyday Science MCQs with Answers

571. 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.

572. 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.

573. Rate of evaporation of petrol is greater than that of water at room temperature because:

• A. petrol molecules do not have any hydrogen bond
• B. petrol is an organic compound
• C. water molecules have small size
• D. petrol molecules have greater size

Explanation: Water molecules form extensive hydrogen bonds, which hold them together strongly and reduce evaporation. Petrol lacks this hydrogen-bond network, so its molecules escape more readily at room temperature.

574. Honey contain glucose and fructose along with some other ingredients, it has greater viscosity due to____________?

• A. hydrogen bonding
• B. irregular shape of the molecules
• C. irregular shape of the molecules and strong inter-molecular forces
• D. greater molecular size

Explanation: Glucose and fructose molecules form many hydrogen bonds and other intermolecular attractions, while their irregular structures hinder smooth flow. These effects together give honey its high viscosity.

575. All of the following substances are crystalline except_____________?

• A. Ice
• B. Diamond
• C. Sucrose
• D. Plastic

Explanation: Ice, diamond and sucrose have ordered crystal structures. Ordinary plastic is generally amorphous, with polymer chains lacking a regular long-range arrangement, so it is the exception.

576. Some substances are good conductor of electricity in both the solid and liquid states. These substances are generally______________?

• A. ionic substances
• B. metallic substances
• C. molecular solids
• D. covalent network solids

Explanation: Metals conduct in the solid state through mobile electrons and remain conductive when molten. Ionic substances generally conduct only when molten or dissolved because their ions must be free to move.

577. Which of the following is a substance?

• A. Sea water
• B. Brass
• C. Tape water
• D. Graphite
• E. Sand

Explanation: Graphite is a pure allotrope of carbon with a definite chemical composition, so it is a substance. Seawater, tap water, brass and sand are mixtures of different components.

578. An atom is_____________?

• A. smallest indivisible particle in an element
• B. smallest particle of an element which can undergo a chemical reaction
• C. building block of an element
• D. always smaller than molecule

Explanation: An atom is the smallest unit of an element that retains its chemical identity and can participate in chemical reactions. It is not indivisible, because it contains subatomic particles.

579. Water is a universal solvent for what reactions?

• A. Chemical
• B. Biochemical
• C. Physical
• D. Nuclear

Explanation: Water dissolves many ionic and polar substances and provides the medium in which most biochemical reactions occur. This is why it is commonly called the universal solvent in biological systems.

580. A glass chimney stops an oil lamp from smoking because:

• A. It increases the supply of oxygen to the flame by convection
• B. The heat produced ensures complete
• C. Both to these
• D. Neither of these

Explanation: A glass chimney promotes convection, drawing more oxygen to the flame, and the improved air supply supports more complete combustion with less soot. Thus both stated effects are involved.