Laws of Chemical Combination NDA Questions

NDA Chemistry

Laws of Chemical Combination MCQ Questions


1.
Who proposed the Law of Conservation of Mass and in which year?
A.
Antoine Lavoisier (French chemist), 1789
B.
John Dalton, 1808
C.
Joseph Proust, 1799
D.
Gay-Lussac, 1808
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ANSWER :
A. Antoine Lavoisier (French chemist), 1789
2.
Which of the following is the correct statement of the Law of Conservation of Mass?
A.
The total number of molecules is conserved in every chemical reaction
B.
Energy and mass are always converted into each other during a chemical reaction
C.
Matter can neither be created nor destroyed in a chemical reaction — the total mass of all reactants equals the total mass of all products
D.
The volume of reactants always equals the volume of products in all reactions
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ANSWER :
C. Matter can neither be created nor destroyed in a chemical reaction — the total mass of all reactants equals the total mass of all products
3.
Lavoisier demonstrated the Law of Conservation of Mass using which key experimental setup?
A.
He melted metals in an open furnace and weighed the ash produced
B.
He heated mercury oxide and collected the gas liberated
C.
He burned wood in excess oxygen and measured the light emitted
D.
He performed reactions in a closed container (sealed flask) and weighed reactants and products carefully before and after the reaction
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ANSWER :
D. He performed reactions in a closed container (sealed flask) and weighed reactants and products carefully before and after the reaction
4.
Which of the following chemical reactions illustrates the Law of Conservation of Mass?
A.
Mg + O₂ → MgO; magnesium loses mass as it burns
B.
2H₂O → H₂ + O₂; mass of water completely converts to energy
C.
C + O₂ → CO₂; carbon becomes lighter after burning in oxygen
D.
CaCO₃ → CaO + CO₂; if 100 g CaCO₃ decomposes, 56 g CaO + 44 g CO₂ are produced (56 + 44 = 100 g — total mass conserved)
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ANSWER :
D. CaCO₃ → CaO + CO₂; if 100 g CaCO₃ decomposes, 56 g CaO + 44 g CO₂ are produced (56 + 44 = 100 g — total mass conserved)
5.
Who formulated the Law of Definite Proportions (Law of Constant Composition) and when?
A.
Joseph Proust (French chemist), 1799
B.
John Dalton, 1808
C.
Gay-Lussac, 1808
D.
Antoine Lavoisier, 1789
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ANSWER :
A. Joseph Proust (French chemist), 1799
6.
What is the correct statement of the Law of Definite Proportions (also called Law of Constant Composition)?
A.
The relative number of moles of elements in a compound changes with temperature
B.
A compound always contains elements in whole number ratios by number of atoms
C.
The volume ratio of elements in a compound is always a simple whole number
D.
A given compound always contains exactly the same elements combined together in the same fixed proportion by mass, regardless of its source or method of preparation
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ANSWER :
D. A given compound always contains exactly the same elements combined together in the same fixed proportion by mass, regardless of its source or method of preparation