NEET Practice Questions (MCQs) with Answers & Solutions

The NCERT states, 'nuclear charge increases from scandium to zinc but electrons are added to the orbital of inner subshell, i.e., 3d orbitals. These 3d electrons shield the 4s electrons from the increasing nuclear charge somewhat more effectively than the outer shell electrons can shield one another. Therefore, the atomic radii decrease less rapidly. Thus, ionization energies increase only slightly along the 3d series.'

The NCERT explicitly states, 'However, the trend of steady increase in second and third ionisation enthalpy breaks for the formation of Mn$^{2+}$ and Fe$^{3+}$ respectively. In both the cases, ions have d$^{5}$ configuration.' While d$^{10}$ and d$^{0}$ are stable, the context specifically mentions the d$^{5}$ configuration of Mn$^{2+}$ causing a 'break' in the steady increasing trend of ionization enthalpy. The stability of Sc$^{3+}$ (d$^{0}$) means its value for the $E°(M^{3+}/M^{2+})$ reduction potential is low, reflecting its stability, but not described as an anomaly in the general trend of increasing ionization enthalpies at that point.

Lithium is an alkali metal (minima on the graph in Fig. 3.5), known for its low ionization enthalpy due to its larger atomic radius, a single loosely bound valence electron in the outermost s-orbital, and the associated high reactivity. All factors contribute to its lower ionization enthalpy compared to its period neighbors.

The NCERT text states: 'The use of vaccines and immunisation programmes have enabled us to completely eradicate a deadly disease like smallpox.' This highlights smallpox as the disease successfully eradicated by vaccination efforts.

According to the NCERT text, 'The principle of immunisation or vaccination is based on the property of ‘memory’ of the immune system.' This memory allows for a quicker and more intense response upon subsequent exposure to the same pathogen.

The NCERT text specifies: 'In vaccination, a preparation of antigenic proteins of pathogen or inactivated/weakened pathogen (vaccine) are introduced into the body.' This exposure stimulates the body's own immune response.

The NCERT states: 'The antibodies produced in the body against these antigens would neutralise the pathogenic agents during actual infection.' Vaccines train the immune system to produce these protective antibodies.

The NCERT explains, 'The vaccines also generate memory – B and T-cells that recognise the pathogen quickly on subsequent exposure and overwhelm the invaders with a massive production of antibodies.' These memory cells are key for long-term immunity.

The NCERT states: 'If a person is infected with some deadly microbes to which quick immune response is required as in tetanus, we need to directly inject the preformed antibodies, or antitoxin... Even in cases of snakebites... contain preformed antibodies... This type of immunisation is called passive immunisation.'

The NCERT mentions: 'A large number of other infectious diseases like polio, diphtheria, pneumonia and tetanus have been controlled to a large extent by the use of vaccines.' Pneumonia is listed among these.