Chemistry MCQs for NEET — Practice Questions with Answers

The NCERT text describes, 'A modern version, the so-called 'long form' of the Periodic table of the elements (Fig. 3.2), is the most convenient and widely used. The horizontal rows (which Mendeleev called series) are called periods and the vertical columns, groups. Elements having similar outer electronic configurations in their atoms are arranged in vertical columns, referred to as groups or families.'

The context states, 'According to the recommendation of International Union of Pure and Applied Chemistry (IUPAC), the groups are numbered from 1 to 18 replacing the older notation of groups IA … VIIA, VIII, IB … VIIB and 0.'

According to the NCERT text, 'These reagents are obtained by the reaction of haloalkanes with magnesium metal in dry ether.' The presence of moisture would lead to the decomposition of the Grignard reagent.

The NCERT states, 'Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons. Even water, alcohols, amines are sufficiently acidic to convert them to corresponding hydrocarbons.' Anhydrous diethyl ether is the solvent used for its preparation and does not contain active protons to react with the Grignard reagent.

The NCERT text explicitly states, 'In the Grignard reagent, the carbon-magnesium bond is covalent but highly polar, with carbon pulling electrons from electropositive magnesium; the magnesium halogen bond is essentially ionic.'

The NCERT states, 'In the Grignard reagent, the carbon-magnesium bond is covalent but highly polar'. The statement that it is 'primarily ionic' is incorrect; the magnesium-halogen bond is essentially ionic.

Grignard reagents react with any source of proton (or deuteron in this case) to give hydrocarbons. $CH_3MgI$ will abstract a deuteron from $D_2O$ to form $CH_3D$ (deutero-methane), and not methane or iodomethane. The NCERT implies this by stating 'react with any source of proton to give hydrocarbons'.

The NCERT states, 'Alkyl halides react with sodium in dry ether to give hydrocarbons containing double the number of carbon atoms present in the halide. This reaction is known as Wurtz reaction.'

According to the Wurtz reaction, alkyl halides form hydrocarbons with double the number of carbon atoms. If methyl bromide ($CH_3Br$) is used, the product will have $1 imes 2 = 2$ carbon atoms, which corresponds to ethane ($CH_3CH_3$). The NCERT defines the Wurtz reaction as giving 'hydrocarbons containing double the number of carbon atoms present in the halide'.

The NCERT text specifies, 'Alkyl halides react with sodium in dry ether to give hydrocarbons... This reaction is known as Wurtz reaction.'