NEET Practice Questions (MCQs) with Answers & Solutions

In methods like the one from benzenesulphonic acid or haloarenes, sodium phenoxide is formed. Acidification (e.g., with dilute acid) is used to protonate the phenoxide ion ($C_6H_5O^-$) to regenerate the neutral phenol ($C_6H_5OH$). The NCERT states, 'Acidification of the sodium salt gives phenol.'

The NCERT text specifies, 'A diazonium salt is formed by treating an aromatic primary amine with nitrous acid ($NaNO_2 + HCl$) at 273-278 K.' This low temperature range (0-5 °C) is crucial for the stability of diazonium salts.

The NCERT clearly mentions, 'Most of the worldwide production of phenol is from cumene.'

The NCERT states, 'In the laboratory, phenols are prepared from benzene derivatives by any of the following methods' and then lists methods like from haloarenes, benzenesulphonic acid, and diazonium salts, all of which involve replacing existing groups on the benzene ring with a hydroxyl group either directly or indirectly.

The NCERT specifies, 'Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide.'

The NCERT states, 'It (cumene hydroperoxide) is converted to phenol and acetone by treating it with dilute acid. Acetone, a by-product of this reaction, is also obtained in large quantities by this method.'

According to Newton's second law, F(t) = ma(t). For SHM, acceleration a(t) = -ω²x(t). Substituting this into Newton's second law gives F(t) = -mω²x(t). The text also defines k = mω², so F(t) = -kx(t). Therefore, all the given options are correct representations of the force law for SHM. (NCERT, page 267)

The context states: 'Like acceleration, force is always directed towards the mean position—hence it is sometimes called the restoring force in SHM.' This is a fundamental characteristic of SHM. (NCERT, page 267)

The context states: 'Note that the force in Eq. (13.13) is linearly proportional to x(t). A particle oscillating under such a force is, therefore, calling a linear harmonic oscillator.' (NCERT, page 267)

The text explains: 'In the real world, the force may contain small additional terms proportional to x², x³, etc. These then are called non-linear oscillators.' (NCERT, page 267)