NEET Practice Questions (MCQs) with Answers & Solutions

Allylic halides are defined as compounds 'in which the halogen atom is bonded to an sp$^3$-hybridised carbon atom adjacent to carbon-carbon double bond (C=C)'.

Although not explicitly stated as a formula within the provided snippets, bond polarity (which contributes to dipole moment) is directly related to electronegativity difference, and dipole moment itself is a product of charge separation and bond length ($μ = q imes d$). The NCERT text mentions 'some typical bond lengths, bond enthalpies and dipole moments are given in Table 6.2', implying these are related properties.

The NCERT text states, 'Instability of phenyl cation: In case of haloarenes, the phenyl cation formed as a result of self-ionisation will not be stabilised by resonance and therefore, S$_N$1 mechanism is ruled out.' This contributes to their lower reactivity in nucleophilic substitution.

While the provided text doesn't directly state the trend for bond enthalpy, it mentions 'Some typical bond lengths, bond enthalpies and dipole moments are given in Table 6.2.' Generally, as bond length increases (due to increasing atomic size), bond strength (and thus bond enthalpy) decreases. For example, C-F bonds are typically stronger than C-I bonds. This is a common chemical principle that a NEET student is expected to know to interpret tabulated data.

The NCERT text states that stopping distance depends on initial velocity ($v_0$) and braking capacity (deceleration, $-a$). While reaction time contributes to the total stopping distance (reaction distance + braking distance), the stopping distance specifically refers to the distance traveled after brakes are applied, which is primarily influenced by initial velocity and deceleration. The formula provided, $d_s = -v_0^2 / (2a)$, does not include mass. Although mass affects the deceleration for a given braking force, the question asks about factors directly influencing the stopping distance given a deceleration.

According to the NCERT text, 'Thus, the stopping distance is proportional to the square of the initial velocity. Doubling the initial velocity increases the stopping distance by a factor of 4 (for the same deceleration).' This is derived from the formula $d_s = -v_0^2 / (2a)$. If $v_0$ becomes $2v_0$, then $d_s$ becomes $(2v_0)^2 / (2a) = 4v_0^2 / (2a)$, which is 4 times the original stopping distance.

The NCERT text states, 'Reaction time depends on complexity of the situation and on an individual.' Factors like fatigue, distraction, or intoxication (e.g., alcohol) would impair an individual's ability to observe, think, and act quickly, thereby increasing reaction time. The other options describe conditions that would likely lead to a decreased or normal reaction time.

The NCERT example states, 'The ruler drops under free fall. Therefore, $v_0 = 0$, and $a = -g = -9.8 \text{ m s}^{-2}$. The distance travelled $d$ and the reaction time $t_r$ are related by $d = \frac{1}{2} g t_r^2$.' This is derived from the equation of motion for constant acceleration, $s = ut + \frac{1}{2}at^2$, where initial velocity $u=0$, acceleration $a=g$, and distance $s=d$.

The NCERT text provides data: 'the braking distance was found to be 10 m, 20 m, 34 m and 50 m corresponding to velocities of 11, 15, 20 and 25 m/s'. Therefore, for a velocity of $25 \text{ m/s}$, the braking distance is $50 \text{ m}$ based on the given empirical data.

The NCERT text explicitly states, 'Stopping distance is an important factor considered in setting speed limits, for example, in school zones.' The primary reason for lower speed limits in areas like school zones is to allow drivers more time and distance to stop if unexpected situations (like a child running onto the road) arise, thereby enhancing safety.