Chemistry MCQs for NEET — Practice Questions with Answers

Archeobacteria, also known as archaea, are extremophiles that can survive in extreme conditions, including high temperatures. They thrive in environments such as hot springs and hydrothermal vents, where temperatures can reach as high as 110 °C. Therefore, the correct answer is 'All of these' as archeobacteria can survive at 90 °C, 100 °C, and 110 °C.

rate doubles with every 10 degree celcius increase in temperature and decreases  by half with  decrease in 10 degree celcius 

Orchids are known for having seeds that do not contain stored food. Unlike many seeds, orchid seeds are very small and lack endosperm, which is the tissue that provides nutrients to the developing plant embryo. This is why orchid seeds are often dependent on symbiotic relationships with fungi to germinate and grow.

All animals and humans store some glucose in the cells so that it is available for quick shots of energy. When there is excess of glucose in the body, it is stored in the liver as the large compound called glycogen.

Because dimension of invar does not vary with temperature.

Maxmimum density of water is at $ 40 ^\circ C $ also $ { C \over 5} = { F -32 \over 9 } $

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.

Carbon shows tetravalency in its excited state. In its ground state, carbon has the electronic configuration $1s^2 2s^2 2p^2$. In the excited state, one of the 2s electrons is promoted to the 2p orbital, resulting in the configuration $1s^2 2s^1 2p^3$. This allows carbon to form four covalent bonds, utilizing one electron from the 2s orbital and three electrons from the 2p orbitals, making it tetravalent.