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Some Basic Concepts in Chemistry MCQs for NEET — Chemistry Questions with Answers

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In each of the follwoing questions, two statements are given, one is Assertion (A) and the other is Reason (R). Examine the statements carefully and mark the correct answer according to the instructions given below : A : In the equation $ NH_ 3 + HCl \rightarrow NH_4 Cl, , Gay-Lussac’s law is not applicable to NH_4Cl $ . R : $ NH_4Cl$ is not a gas,.

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Explanation

Gay-Lussac's law states that gases combine or are produced in volumes that bear a simple ratio to one another. Since NH4Cl is a solid, not a gas, Gay-Lussac's law is not applicable to it. Both the assertion and reason are correct, and the reason correctly explains the assertion.

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In each of the follwoing questions, two statements are given, one is Assertion (A) and the other is Reason (R). Examine the statements carefully and mark the correct answer according to the instructions given below : A : Atomic mass of sodium is 23 u. R : An atom of sodium is 23 times heavier than an atom of $ {12} ^ C $

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In each of the follwoing questions, two statements are given, one is Assertion (A) and the other is Reason (R). Examine the statements carefully and mark the correct answer according to the instructions given below : A: Pure water, irrespective of its source always contain hydrogen and oxygen in the ratio 1 : 8 bymass. R : Total mass of reactants and products remains constant during physical or chemical change

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Explanation

The statement A is correct as pure water always contains hydrogen and oxygen in the ratio of 1:8 by mass. The statement R is also correct as the total mass of reactants and products remains constant during a chemical reaction. However, R is not the correct explanation for A.

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In each of the follwoing questions, two statements are given, one is Assertion (A) and the other is Reason (R). Examine the statements carefully and mark the correct answer according to the instructions given below : A : Mass numbers of most of the elements are fractional. R: Mass numbers are obtained by comparing with mass number of $ {12} ^ C $ .

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Explanation

Both statements A and R are incorrect. Mass numbers of elements are always whole numbers and not fractional. Mass numbers are determined by comparing with the mass of a carbon-12 atom, which is assigned a mass number of 12 exactly.

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In each of the follwoing questions, two statements are given, one is Assertion (A) and the other is Reason (R). Examine the statements carefully and mark the correct answer according to the instructions given below : A : The mass of the products formed in a reaction depends upon the limting reactant. R: Limting reactant reacts completely in the reaction.

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Explanation

The mass of products formed in a reaction depends on the limiting reactant because the limiting reactant gets consumed completely. The other reactants remain in excess.

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In each of the follwoing questions, two statements are given, one is Assertion (A) and the other is Reason (R). Examine the statements carefully and mark the correct answer according to the instructions given below : A : Cinnabar is a chemical compound whereas brass is mixture. R : Cinnabar always contain 6.25 times mercury than sulplur by weight. Brass can have any proportion of Cu and Zn.

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Explanation

Cinnabar is a chemical compound (HgS) with a fixed composition, while brass is an alloy (mixture) of copper and zinc in varying proportions. The statement about cinnabar's composition is correct.

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In each of the follwoing questions, two statements are given, one is Assertion (A) and the other is Reason (R). Examine the statements carefully and mark the correct answer according to the instructions given below : A : $1 L of O_2 and 1 L of O_3 $ contains the same number of moles under identical conditions. R : Under identical conditions, $1 L of O_2 and 1 L of O_3 $ contain the same number of oxygen atoms

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Explanation

The assertion that 1L of O2 and 1L of O3 contain the same number of moles under identical conditions is correct, as the mole is a measure of the amount of substance. However, the reason is incorrect because O3 has more oxygen atoms per molecule compared to O2.

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In each of the follwoing questions, two statements are given, one is Assertion (A) and the other is Reason (R). Examine the statements carefully and mark the correct answer according to the instructions given below : A : The standard unit for expressing atomic mass is amu. R : Now a days amu is represented by ‘u’.

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Explanation

The assertion that the standard unit for expressing atomic mass is amu (atomic mass unit) is correct. The reason that nowadays amu is represented by 'u' is also correct, but it does not explain the assertion. The unit 'u' is simply a modern representation of the same atomic mass unit.

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Calculate percentage of $ NO_2 by weight in N_2O_4 $ which has vapour density of 36.

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How many grams of concentrated nitric acid solution should be used to prepare 250 mL of 2.0 M HNO3? The concentrated acid is 70% HNO3.

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Explanation

(a) Given, molarity of solution=2

Volume of solution = 250mL=250/1000=1/4L

Molar mass of HNO3 = 1+14+3x16=63g mol-1

Molarity = weight of HNO3Molecular mass  of HNO3×volume of solution(L)

Weight of  HNO3 = molarity x molecular massx volume(L) = 2x63x1/4g=31.5g

It is the weight of 100%  HNO3

But the given acid is 70% HNO3

Its weight = 31.5x100/70g=45g

 

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