NEET Practice Questions (MCQs) with Answers & Solutions

The text states: 'For C (diamond), Si and Ge, the energy gaps are 5.4 eV, 1.1 eV and 0.7 eV, respectively. Sn also is a group IV element but it is a metal because the energy gap in its case is 0 eV.' Therefore, $E_g > 3 \text{ eV}$ for Sn is incorrect.

The text defines: 'The energy band which includes the energy levels of the valence electrons is called the valence band.'

The context states: 'In extrinsic semiconductors, because of the abundance of majority current carriers, the minority carriers produced thermally have more chance of meeting majority carriers and thus getting destroyed. Hence, the dopant, by adding a large number of current carriers of one type, which become the majority carriers, indirectly helps to reduce the intrinsic concentration of minority carriers.'

The text clearly explains this for semiconductors: 'Here a finite but small band gap ($E_g < 3 \text{ eV}$) exists. Because of the small band gap, at room temperature some electrons from valence band can acquire enough energy to cross the energy gap and enter the conduction band.' This implies easier transition for smaller $E_g$, leading to conduction.

The 'POINTS TO PONDER' section states: 'The energy bands ($E_C$ or $E_V$) in the semiconductors are space delocalised which means that these are not located in any specific place inside the solid. The energies are the overall averages. When you see a picture in which $E_C$ or $E_V$ are drawn as straight lines, then they should be respectively taken simply as the bottom of conduction band energy levels and top of valence band energy levels.'

The NCERT summary states: 'Aschelminthes are pseudocoelomates and include parasitic as well as non-parasitic roundworms.' This directly answers the question about their body cavity.

The NCERT summary mentions: 'Aschelminthes are pseudocoelomates and include parasitic as well as non-parasitic roundworms.' This clearly defines them as roundworms.

The text states: 'A still higher level of organisation, i.e., organ level is exhibited by members of Platyhelminthes and other higher phyla where tissues are grouped together to form organs, each specialised for a particular function.' Aschelminthes are considered a 'higher phyla' than sponges and coelenterates and exhibit organ-system level, but among the given options, Platyhelminthes is the first to show organ level.

The NCERT summary states: 'Aschelminthes are pseudocoelomates and include parasitic as well as non-parasitic roundworms.' This is a defining characteristic of the phylum. Suckers and hooks are characteristic of parasitic Platyhelminthes, metameric segmentation is for Annelida, and calcareous shell for Mollusca.

The NCERT summary explicitly states: 'Aschelminthes are pseudocoelomates and include parasitic as well as non-parasitic roundworms.'