NEET Practice Questions (MCQs) with Answers & Solutions

The text states: 'Internal energy U of a system is an example of a thermodynamic ‘state variable’ – its value depends only on the given state of the system, not on history i.e. not on the ‘path’ taken to arrive at that state.' In another section, it lists 'change in internal energy, ∆U, depends on initial and final states only and is a state function'.

The context states: 'Temperature is a marker of the ‘hotness’ of a body. It determines the direction of flow of heat when two bodies are placed in thermal contact.'

The context states: 'On contact between a hot body and a cold body, the fluid (called caloric) flowed from the colder to the hotter body!'

The text mentions: 'A most natural explanation of the observations was that heat was a form of energy and the experiment demonstrated conversion of energy from one form to another–from work to heat.' It also noted that 'the amount of heat produced depended on the work done... but not on the sharpness of the drill' contradicting the caloric theory.

The context states: 'Thus, it includes only the (disordered) energy associated with the random motion of molecules of the system.'

The context asks: 'how to assign numerical values to temperatures of different bodies ? In other words, how do we construct a scale of temperature ? Thermometry deals with this basic question...'

The context states: 'The distinction between mechanics and thermodynamics is worth bearing in mind. In mechanics, our interest is in the motion of particles or bodies under the action of forces and torques. Thermodynamics is not concerned with the motion of the system as a whole. It is concerned with the internal macroscopic state of the body.'

The C-O bond in ethers can be cleaved by hydrogen halides. In the case of an alkyl-aryl ether like anisole, the cleavage occurs such that the halide attacks the alkyl group. The context states 'the attack by I- ion breaks O–CH3 bond to form CH3I. Phenols do not react further to give halides because the $sp^2$ hybridised carbon of phenol cannot undergo nucleophilic substitution reaction needed for conversion to the halide.' Thus, phenol and iodomethane are formed.

The NCERT text explicitly states, 'The alkoxy group (-OR) is ortho, para directing and activates the aromatic ring towards electrophilic substitution in the same way as in phenol.'

The context mentions, 'anisole undergoes bromination with bromine in ethanoic acid even in the absence of iron (III) bromide catalyst. It is due to the activation of benzene ring by the methoxy group.' This activation makes the ring sufficiently electron-rich to react with the electrophile without a stronger catalyst.