NEET Practice Questions (MCQs) with Answers & Solutions

The NCERT biographical note states, 'While attempting to find an efficient catalyst for the process of methylation, he noted that Zn in diethyl ether had been used for this purpose and wondered whether the Mg/ether combination might be successful.'

The synthesis of toluene from bromobenzene (an aryl halide) and methyl bromide (an alkyl halide) using sodium in dry ether fits the description of the Wurtz-Fittig reaction: 'A mixture of an alkyl halide and aryl halide gives an alkylarene when treated with sodium in dry ether and is called Wurtz-Fittig reaction.'

Diphenyl consists of two phenyl groups joined together. This outcome is characteristic of the Fittig reaction, which uses 'Aryl halides also give analogous compounds when treated with sodium in dry ether, in which two aryl groups are joined together. It is called Fittig reaction.'

According to the NCERT text under '6.1.5 General Characteristics of Equilibria Involving Physical Processes', point (iii) states: 'All measurable properties of the system remain constant.' Option 1 is incorrect because equilibrium is possible only in a closed system. Option 2 is incorrect because opposing processes occur at the same rate, and the condition is dynamic but stable. Option 4 is incorrect because the magnitude of such quantities at any stage indicates the extent to which the physical process has proceeded before reaching equilibrium.

The NCERT text states: 'When the rates of the forward and reverse reactions become equal, the concentrations of the reactants and the products remain constant. This is the stage of chemical equilibrium. This equilibrium is dynamic in nature...' Options 1 and 4 describe specific cases of equilibrium, not a general characteristic. Option 2 contradicts the dynamic nature of equilibrium.

The NCERT text specifically states: 'Thus, at equilibrium, the rate of evaporation is equal to the rate of condensation.' This indicates a dynamic equilibrium where opposing processes occur at equal rates.

The NCERT text mentions: 'The dynamic nature of chemical equilibrium can be demonstrated in the synthesis of ammonia by Haber’s process... In order to understand the dynamic nature of the reaction, synthesis of ammonia is carried out with exactly the same starting conditions (of partial pressure and temperature) but using $ ext{D}_2$ (deuterium) in place of $ ext{H}_2$ ... This is not feasible in a school laboratory. However this concept can be easily comprehended by performing the following activity.' And from the summary 'When the number of molecules leaving the liquid to vapour equals the number of molecules returning to the liquid from vapour, equilibrium is said to be attained and is dynamic in nature.' The example of using $ ext{D}_2$ in Haber's process and the suggested activity using colored water (where transfer continues even after levels are constant) both point to continuous microscopic activity, even when macroscopic properties are constant. Directly, 'The dynamic nature of chemical equilibrium can be demonstrated by the use of radioactive isotopes.' is mentioned in the 'Dynamic Equilibrium – A Student’s Activity' section.

The NCERT text states: 'The equilibrium equation is also known as the law of mass action because in the early days of chemistry, concentration was called “active mass”.' It refers specifically to the equilibrium constant expression ($K_c = ext{[C]}^c ext{[D]}^d/ ext{[A]}^a ext{[B]}^b$).

The NCERT text clearly states: 'When the rates of the forward and reverse reactions become equal, the concentrations of the reactants and the products remain constant. This is the stage of chemical equilibrium.'

The NCERT summary states: 'Catalyst does not effect the equilibrium composition of a reaction mixture but increases the rate of chemical reaction by making available a new lower energy pathway for conversion of reactants to products and vice-versa.' Temperature, pressure, and concentration all influence the equilibrium position according to Le Chatelier's principle.