Chemistry MCQs for NEET — Practice Questions with Answers

While the text (The d - and f - Block Elements, page 102) states that for the first series transition metals the contribution of the orbital angular momentum is effectively quenched, Table 4.7 shows slight discrepancies between 'Calculated' and 'Observed' magnetic moments. These small differences are often attributed to the incomplete quenching of orbital angular momentum in some cases, or other complex interactions not accounted for by the simple 'spin-only' formula, which considers only spin contribution. The question from coordination compounds 5.7: '[Fe(H2O)6]3+ is strongly paramagnetic whereas [Fe(CN)6]3– is weakly paramagnetic. Explain.' highlights that environmental factors can influence magnetic properties.

The text (MAGNETISM_AND_MATTER, page 148, and page 152 summary point 6) states: 'Diamagnetism is present in all the substances. However, the effect is so weak in most cases that it gets shifted by other effects like paramagnetism, ferromagnetism, etc.' and 'Diamagnetism is universal. It is present in all materials. But it is weak and hard to detect if the substance is para- or ferromagnetic.'

The text explains (MAGNETISM_AND_MATTER, page 148): 'When magnetic field is applied, those electrons having orbital magnetic moment in the same direction slow down and those in the opposite direction speed up. This happens due to induced current in accordance with Lenz’s law...'

According to the NCERT text, 'These earlier ideas were mere speculations and there was no way to test them experimentally. These ideas remained dormant for a very long time and were revived again by scientists in the nineteenth century.' This indicates that before Dalton, atomic theories were speculative.

The NCERT text states, 'The atomic theory of matter was first proposed on a firm scientific basis by John Dalton, a British school teacher in 1808.'

The text states, 'Dalton’s atomic theory was able to explain the law of conservation of mass, law of constant composition and law of multiple proportion very successfully.' The other options are later developments in atomic theory or physics.

Dalton's first postulate was 'Matter consists of indivisible atoms.' However, the text indicates, 'Towards the end of the nineteenth century, it was proved experimentally that atoms are divisible and consist of three fundamental particles: electrons, protons and neutrons.'

The NCERT states, 'The existence of atoms has been proposed since the time of early Indian and Greek philosophers (400 B.C.) who were of the view that atoms are the fundamental building blocks of matter.'

The text explicitly states: 'For example, questions like why two or more atoms combine to form molecules, why some elements are metals while others are non-metals, why elements like helium and argon are not reactive but elements like the halogens are reactive, find simple explanation from the electronic configuration. These questions have no answer in the Daltonian model of atom.'

According to the NCERT text, 'The –OH group attached to the benzene ring activates it towards electrophilic substitution. Also, it directs the incoming group to ortho and para positions in the ring as these positions become electron rich due to the resonance effect caused by –OH group.' Therefore, directing to meta positions is incorrect.