Q1
What is the chemical formula of common salt?
- (1)KCl
- (2)NaCl✓ Correct answer
- (3)Na₂CO₃
- (4)CaCl₂
Answer: (2) NaCl
Explanation
Common salt is sodium chloride, NaCl.
Chemistry MCQ with Answers
20 questionswith explanationsfor RAS, Patwari, VDO and other Rajasthan exams
Questions
Q2
What is the pH of pure water at 25°C?
- (1)7✓ Correct answer
- (2)0
- (3)14
- (4)5
Answer: (1) 7
Explanation
Pure water is neutral and has a pH of 7 at 25°C.
Q3
Which gas is released when a metal like zinc reacts with dilute hydrochloric acid?
- (1)Oxygen
- (2)Carbon dioxide
- (3)Chlorine
- (4)Hydrogen✓ Correct answer
Answer: (4) Hydrogen
Explanation
Zn + 2HCl → ZnCl₂ + H₂; active metals displace hydrogen gas from dilute acids.
Q4
Which is the most abundant gas in the Earth's atmosphere?
- (1)Oxygen
- (2)Carbon dioxide
- (3)Nitrogen✓ Correct answer
- (4)Argon
Answer: (3) Nitrogen
Explanation
Nitrogen makes up about 78% of the atmosphere by volume, followed by oxygen (about 21%).
Q5
What is the chemical name of baking soda?
- (1)Sodium hydrogen carbonate✓ Correct answer
- (2)Sodium carbonate
- (3)Calcium carbonate
- (4)Sodium hydroxide
Answer: (1) Sodium hydrogen carbonate
Explanation
Baking soda is sodium hydrogen carbonate (sodium bicarbonate), NaHCO₃.
Q6
What is the chemical formula of Plaster of Paris?
- (1)CaSO₄·2H₂O
- (2)CaCO₃
- (3)CaOCl₂
- (4)CaSO₄·½H₂O✓ Correct answer
Answer: (4) CaSO₄·½H₂O
Explanation
Plaster of Paris is calcium sulphate hemihydrate, CaSO₄·½H₂O; CaSO₄·2H₂O is gypsum.
Q7
Rusting of iron requires the presence of which of the following?
- (1)Only oxygen
- (2)Both oxygen and water (moisture)✓ Correct answer
- (3)Only water
- (4)Nitrogen and water
Answer: (2) Both oxygen and water (moisture)
Explanation
Iron rusts only when both oxygen (air) and moisture are present, forming hydrated iron(III) oxide.
Q8
What is the atomic number of carbon?
- (1)12
- (2)8
- (3)6✓ Correct answer
- (4)14
Answer: (3) 6
Explanation
Carbon has 6 protons, so its atomic number is 6; 12 is its common mass number.
Q9
Which of the following is a noble (inert) gas?
- (1)Nitrogen
- (2)Chlorine
- (3)Hydrogen
- (4)Argon✓ Correct answer
Answer: (4) Argon
Explanation
Argon belongs to Group 18 (noble gases), along with helium, neon, krypton, xenon and radon.
Q10
What is the chemical formula of bleaching powder (calcium oxychloride)?
- (1)CaCl₂
- (2)CaOCl₂✓ Correct answer
- (3)Ca(OH)₂
- (4)CaCO₃
Answer: (2) CaOCl₂
Explanation
Bleaching powder is CaOCl₂, made by passing chlorine gas over dry slaked lime.
Q11
Which metal is a liquid at room temperature?
- (1)Mercury✓ Correct answer
- (2)Sodium
- (3)Aluminium
- (4)Tin
Answer: (1) Mercury
Explanation
Mercury (Hg) has a melting point of about −39°C, so it is liquid at room temperature; sodium, aluminium and tin are solids.
Q12
What is the chemical formula of washing soda?
- (1)NaHCO₃
- (2)NaOH
- (3)Na₂CO₃·10H₂O✓ Correct answer
- (4)Na₂SO₄
Answer: (3) Na₂CO₃·10H₂O
Explanation
Washing soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O.
Q13
Who discovered the neutron?
- (1)James Chadwick✓ Correct answer
- (2)J. J. Thomson
- (3)Ernest Rutherford
- (4)E. Goldstein
Answer: (1) James Chadwick
Explanation
James Chadwick discovered the neutron in 1932; Thomson discovered the electron and Goldstein discovered canal rays.
Q14
Consider the following statements: 1. Isotopes of an element have the same atomic number but different mass numbers. 2. Isobars have the same mass number but different atomic numbers. 3. Isotopes of an element have nearly identical chemical properties. Which of the statements given above are correct?
- (1)1 and 2 only
- (2)2 and 3 only
- (3)1 and 3 only
- (4)1, 2 and 3✓ Correct answer
Answer: (4) 1, 2 and 3
Explanation
All three are correct; isotopes have the same number of electrons, so their chemical properties are nearly the same.
Q15
What is the electronic configuration (K, L, M, N shells) of the element with atomic number 19?
- (1)2, 8, 9
- (2)2, 9, 8
- (3)2, 8, 8, 1✓ Correct answer
- (4)2, 8, 7, 2
Answer: (3) 2, 8, 8, 1
Explanation
Potassium (Z = 19) has the configuration 2, 8, 8, 1; the outer shell starts filling before M holds more than 8 electrons.
Q16
The Modern Periodic Law states that the properties of elements are a periodic function of their:
- (1)Atomic mass
- (2)Number of neutrons
- (3)Atomic volume
- (4)Atomic number✓ Correct answer
Answer: (4) Atomic number
Explanation
Based on Moseley's work, the Modern Periodic Law uses atomic number; Mendeleev's law was based on atomic mass.
Q17
Consider the following statements about the Modern Periodic Table: 1. On moving from left to right across a period, the atomic radius generally decreases. 2. On moving from left to right across a period, the metallic character increases. Which of the statements given above is/are correct?
- (1)1 only✓ Correct answer
- (2)2 only
- (3)Both 1 and 2
- (4)Neither 1 nor 2
Answer: (1) 1 only
Explanation
Across a period the rising nuclear charge pulls electrons closer, so atomic radius decreases and metallic character also decreases.
Q18
Arrange the following in increasing order of pH: 1. Milk of magnesia 2. Lemon juice 3. 1 M sodium hydroxide solution 4. Pure water
- (1)4, 2, 1, 3
- (2)2, 4, 1, 3✓ Correct answer
- (3)2, 4, 3, 1
- (4)3, 1, 4, 2
Answer: (2) 2, 4, 1, 3
Explanation
Lemon juice is acidic (pH about 2.2), pure water is neutral (7), milk of magnesia is a mild base (about 10) and 1 M NaOH is a strong base (about 14).
Q19
Tooth decay starts when the pH of the mouth falls below about:
- (1)6.5
- (2)7.5
- (3)5.5✓ Correct answer
- (4)8.5
Answer: (3) 5.5
Explanation
Below pH 5.5 the acid formed by bacteria from food corrodes tooth enamel (calcium hydroxyapatite).
Q20
The stinging hairs of nettle leaves inject which acid, causing burning pain?
- (1)Citric acid
- (2)Oxalic acid
- (3)Lactic acid
- (4)Methanoic acid✓ Correct answer
Answer: (4) Methanoic acid
Explanation
Nettle stings (like ant stings) inject methanoic (formic) acid; rubbing a dock leaf, which is basic, gives relief.