NEET Practice Questions (MCQs) with Answers & Solutions

The assertion is that the mass equivalent of 1000 kWh energy is 40 micrograms, which is correct. The reason provided is that it follows from $E=mc^2$, where $c = 3 imes 10^8 ext{m/s}$. This is also correct. To find the mass, we use the equation $E=mc^2$. Given $E = 1000 ext{kWh} = 3.6 imes 10^9 ext{J}$, we get $m = rac{E}{c^2} = rac{3.6 imes 10^9}{(3 imes 10^8)^2} = 4 imes 10^{-8} ext{kg} = 40 ext{micrograms}$. Therefore, both assertion and reason are true, and the reason is the correct explanation of the assertion.

The assertion that the work done by centripetal force is zero is correct because centripetal force acts perpendicular to the direction of displacement, which means no work is done (work done = force × displacement × cos(θ), and θ = 90°). However, the reason provided is incorrect because centripetal force is not along the tangent but rather directed towards the center of the circular path. Hence, the assertion is true, but the reason is false.

The assertion is that linear momentum is conserved in both elastic and inelastic collisions, which is true. The reason states that total energy is conserved in all such collisions. While energy conservation is true in elastic collisions, in inelastic collisions, only the total energy (kinetic energy + potential energy) is conserved, not just kinetic energy. Therefore, while both the assertion and reason are true, the reason does not correctly explain the assertion.

The assertion says that both a stretched spring and a compressed spring have potential energy, which is true. The reason is that work is done against the restoring force in each case, which is also true. When a spring is either stretched or compressed, work is done against the spring's restoring force, storing potential energy in the spring. Therefore, the reason correctly explains the assertion.

Carbon can form covalent bonds. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding. Carbon typically forms four covalent bonds to achieve a full outer shell of electrons, which is known as a stable octet.

Carbon cannot form $ C^{+4} $ or $ C^{-4} $ ions mainly due to the high ionization enthalpy and high electron gain enthalpy required. Ionization enthalpy refers to the energy required to remove electrons, and for carbon to lose four electrons, it would require a very high amount of energy. Similarly, electron gain enthalpy is the energy change when an electron is added to an atom. Adding four electrons to carbon would also require a significant amount of energy, making it highly unfavorable. Therefore, both high ionization enthalpy and high electron gain enthalpy prevent the formation of $ C^{+4} $ or $ C^{-4} $ ions.