CHEMISTRY ⚗️🧪 PART 1 (ADRE)
Here are 20 multiple-choice questions (MCQs) on chemistry with explanations for each answer:
1. **What is the atomic number of carbon?**
A) 6
B) 8
C) 12
D) 14
**Answer: A) 6**
Explanation: The atomic number represents the number of protons in an atom. Carbon has 6 protons.
2. ***What gas is often referred to as "laughing gas"?
A) Nitrous oxide
B) Carbon dioxide
C) Helium
D) Methane
**Answer: A) Nitrous oxide**
Explanation: Nitrous oxide, \( N_2O \), is commonly known as laughing gas due to its euphoric effects when inhaled.
3. **What type of bond is formed when electrons are shared between atoms?**
A) Ionic bond
B) Covalent bond
C) Metallic bond
D) Hydrogen bond
**Answer: B) Covalent bond**
Explanation: A covalent bond involves the sharing of electron pairs between atoms.
4. Which element, at normal temperature, is a liquid?
A) Mercury
B) Iron
C) Gold
D) Silver
**Answer: A) Mercury**
Explanation: Mercury is the only metal that is in liquid form at room temperature.
5. **The pH scale measures the concentration of what in a solution?**
A) Hydrogen ions
B) Hydroxide ions
C) Salt ions
D) Water molecules
**Answer: A) Hydrogen ions**
Explanation: The pH scale measures the hydrogen ion concentration in a solution, determining its acidity or alkalinity.
6. **What is the main component of natural gas?**
A) Methane
B) Ethane
C) Propane
D) Butane
**Answer: A) Methane**
Explanation: Methane, \( CH_4 \), is the primary component of natural gas.
7. **Which of the following is a noble gas?**
A) Nitrogen
B) Oxygen
C) Argon
D) Carbon
**Answer: C) Argon**
Explanation: Argon is a noble gas, which is inert and does not readily react with other elements.
8. **What is the chemical formula for table salt?**
A) \( NaCl \)
B) \( KCl \)
C) \( LiCl \)
D) \( MgCl_2 \)
**Answer: A) \( NaCl \)**
Explanation: Table salt is composed of sodium chloride, \( NaCl \).
9. **Which of the following is not a type of chemical reaction?**
A) Synthesis
B) Decomposition
C) Electrolysis
D) Photosynthesis
**Answer: D) Photosynthesis**
Explanation: Photosynthesis is a biological process, not a chemical reaction type.
10. **What is the molar mass of water, \( H_2O \)?**
A) 16 g/mol
B) 18 g/mol
C) 20 g/mol
D) 22 g/mol
**Answer: B) 18 g/mol**
Explanation: The molar mass of water is the sum of the atomic masses of hydrogen (2 x 1 g/mol) and oxygen (16 g/mol).
11. **Which element is found in the active site of hemoglobin?**
A) Iron
B) Magnesium
C) Calcium
D) Potassium
**Answer: A) Iron**
Explanation: Iron is present in the active site of hemoglobin, allowing it to bind oxygen.
12. **What is the common name for \( H_2SO_4 \)?**
A) Hydrochloric acid
B) Sulfuric acid
C) Nitric acid
D) Acetic acid
**Answer: B) Sulfuric acid**
Explanation: \( H_2SO_4 \) is commonly known as sulfuric acid.
13. **Which of the following is a polymer?**
A) Glucose
B) Starch
C) Ethanol
D) Methane
**Answer: B) Starch**
Explanation: Made up of many glucose units, starch is a polymer.
14. **What is the oxidation state of hydrogen in most compounds?**
A) +1
B) -1
C) 0
D) +2
**Answer: A) +1**
Explanation: In most compounds, hydrogen has an oxidation state of +1.
15. **Which is the lightest element in the periodic table?**
A) Helium
B) Hydrogen
C) Lithium
D) Beryllium
**Answer: B) Hydrogen**
Explanation: Hydrogen is the lightest and simplest element, with an atomic number of 1.
16. **What type of reaction absorbs heat from the surroundings?**
A) Exothermic
B) Endothermic
C) Synthesis
D) Decomposition
**Answer: B) Endothermic**
Explanation: Endothermic reactions absorb heat, causing the surroundings to cool down.
17. Among these, which one is not a greenhouse gas?**
A) Carbon dioxide
B) Methane
C) Oxygen
D) Nitrous oxide
**Answer: C) Oxygen**
Explanation: Oxygen is not a greenhouse gas; it does not trap heat in the atmosphere.
18. **What is the formula for ammonia?**
A) \( NH_3 \)
B) \( NH_4 \)
C) \( NO_2 \)
D) \( N_2H_4 \)
**Answer: A) \( NH_3 \)**
Explanation: Ammonia is a compound with the formula \( NH_3 \).
19. **Which of the following elements is essential for the formation of bones and teeth?**
A) Phosphorus
B) Sodium
C) Chlorine
D) Iodine
**Answer: A) Phosphorus**
Explanation: Phosphorus is essential for the formation and maintenance of bones and teeth.
20. **What is the most abundant gas in the Earth's atmosphere?**
A) Oxygen
B) Nitrogen
C) Carbon dioxide
D) Argon
**Answer: B) Nitrogen**
Explanation: Nitrogen makes up about 78% of the Earth's atmosphere.
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