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Some Basic concepts of chemistry-Objective Questions for Entrance Exams

These 50 objective questions from Some Basic Concepts of Chemistry are carefully curated to reflect the most frequently tested concepts and numerical patterns seen across major competitive examinations such as JEE, NEET, AIIMS, BITSAT, KVPY, Olympiads, and state engineering entrances. Covering foundational ideas like mole concept, stoichiometry, laws of chemical combination, concentration terms, significant figures, and dimensional analysis, this collection progresses from core NCERT-level understanding to higher-order application-based problems. Each question is accompanied by a precise answer and a concise explanation, enabling learners to strengthen conceptual clarity while sharpening exam temperament. Designed for serious aspirants, these MCQs emphasize speed, accuracy, and analytical thinking—essential traits for success in national-level tests. Regular practice with such exam-modelled problems not only reinforces theory but also builds confidence in tackling complex numericals under timed conditions, making this set an indispensable revision resource for Class XI chemistry preparation.

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Exercise

Some Basic concepts of chemistry

by Academia Aeternum

1. The number of significant figures in \(0.004560\) is:
(Exam: IIT-JEE Year: 1998)
2. How many atoms are present in \(18\,g\) of water?
(Exam: AIPMT Year: 2006)
3. Empirical formula mass of glucose \((C_6H_{12}O_6)\) is:
(Exam: NEET Year: 2017)
4. One mole of any substance contains:
(Exam: AIIMS Year: 2004)
5. The mass percent of oxygen in \(HNO_3\) is:
(Exam: IIT-JEE Year: 2001)
6. Which has maximum number of molecules?
(Exam: BITSAT Year: 2012)
7. Limiting reagent controls:
(Exam: IIT-JEE Year: 2003)
8. Density of a gas at STP is proportional to:
(Exam: KVPY Year: 2010)
9. 5.6 L of \(N_2\) at STP corresponds to:
(Exam: AIPMT Year: 2009)
10. Which law explains conservation of mass?
(Exam: IIT-JEE Year: 1995)
11. Moles of electrons in 1 mol \(Na\) atoms:
(Exam: NEET Year: 2018)
12. The percentage purity if 10 g impure \(CaCO_3\) gives 2.24 L \(CO_2\) at STP:
(Exam: IIT-JEE Year: 2004)
13. Which is not a state function?
(Exam: AIIMS Year: 2007)
14. Significant figures in \(2.300\times10^2\):
(Exam: BITSAT Year: 2014)
15. Mole fraction of \(NaCl\) in 1 mol \(NaCl\)+2 mol \(H_2O\):
(Exam: IIT-JEE Year: 2006)
16. The molarity of pure water at \(25^\circ C\) is approximately:
(Exam: IIT-JEE Year: 2002)
17. Which of the following has the highest mass?
(Exam: NEET Year: 2016)
18. The limiting reagent is:
(Exam: IIT-JEE Year: 1999)
19. The number of moles of \(Na^+\) ions in 1 mol \(Na_2CO_3\) is:
(Exam: AIPMT Year: 2010)
20. The molecular mass of a gas is directly proportional to:
(Exam: KVPY Year: 2011)
21. Which pair obeys the law of multiple proportions?
(Exam: IIT-JEE Year: 1996)
22. The SI unit of amount of substance is:
(Exam: AIIMS Year: 2003)
23. How many significant figures are there in \(0.02030\)?
(Exam: BITSAT Year: 2015)
24. Which is an intensive property?
(Exam: NEET Year: 2019)
25. The percentage of nitrogen in urea \((NH_2)_2CO\) is:
(Exam: IIT-JEE Year: 2000)
26. Which quantity remains constant during a chemical reaction?
(Exam: IIT-JEE Year: 1994)
27. The volume occupied by 2 mol of an ideal gas at STP is:
(Exam: AIPMT Year: 2008)
28. Which unit is used for molality?
(Exam: BITSAT Year: 2013)
29. If the empirical formula mass is 30 and molecular mass is 180, the molecular formula is:
(Exam: NEET Year: 2020)
30. Which law explains gaseous volume ratios?
(Exam: IIT-JEE Year: 1997)
31. The number of molecules in 11 g \(CO_2\) is:
(Exam: AIIMS Year: 2005)
32. Which is not a unit of concentration?
(Exam: NEET Year: 2015)
33. Which contains maximum oxygen atoms?
(Exam: IIT-JEE Year: 2001)
34. Avogadro number relates:
(Exam: AIPMT Year: 2007)
35. Which is a derived SI unit?
(Exam: IIT-JEE Year: 1993)
36. The mass of 1 mole of electrons is approximately:
(Exam: KVPY Year: 2012)
37. Which reaction best demonstrates stoichiometry?
(Exam: IIT-JEE Year: 2005)
38. The dimensional formula of molarity is:
(Exam: IIT-JEE Year: 2007)
39. Which statement is correct?
(Exam: NEET Year: 2021)
40. 22 g \(CO_2\) contains how many moles?
(Exam: AIPMT Year: 2005)
41. Which quantity has maximum numerical value?
(Exam: IIT-JEE Year: 2009)
42. The atomic mass unit is defined relative to:
(Exam: AIIMS Year: 2006)
43. Which is an extensive property?
(Exam: NEET Year: 2018)
44. The number of significant figures in \(1.020\times10^{-3}\):
(Exam: BITSAT Year: 2016)
45. Which law explains why gases mix in all proportions?
(Exam: IIT-JEE Year: 1992)
46. The formula of washing soda is:
(Exam: NEET Year: 2014)
47. The number of moles of oxygen atoms in 1 mol \(H_2SO_4\):
(Exam: IIT-JEE Year: 2008)
48. Which quantity is conserved in a chemical reaction?
(Exam: AIPMT Year: 2011)
49. If the density of a gas is doubled at constant temperature, pressure becomes:
(Exam: IIT-JEE Year: 2010)
50. The branch of chemistry dealing with quantitative relationships is:
(Exam: Olympiad Year: Standard)

Frequently Asked Questions

Chemistry is the branch of science that studies composition, structure, properties, and transformations of matter.

Matter is anything that has mass and occupies space.

The SI unit is mole (mol).

One mole contains \(6.022\times10^{23}\) entities.

\(N_A = 6.022\times10^{23}\,mol^{-1}\).

\(1\,u=\frac{1}{12}\)th mass of one \(^{12}C\) atom.

Average mass of atoms relative to \(1/12\)th of \(^{12}C\).

Sum of atomic masses of all atoms in a molecule.

Sum of atomic masses in an ionic compound.

Molar mass \(=\frac{\text{Mass}}{\text{Moles}}\).

Mass of one mole of substance in g mol\(^{-1}\).

\(n=\frac{m}{M}\).

Mass percent of each element in a compound.

\(\%\text{element}=\frac{\text{mass of element}}{\text{molar mass}}\times100\)

Mass is neither created nor destroyed in a chemical reaction.

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