Chemistry of Life Basics
Level 1: Recognition Test
Time Limit: 20 minutes Total Marks: 30
Section A — Multiple Choice (1 mark each)
Choose the single best answer.
Q1. Which subatomic particle carries a negative charge?
- A) Proton
- B) Neutron
- C) Electron
- D) Nucleus
Q2. The atomic number of an element equals the number of:
- A) Neutrons
- B) Protons
- C) Protons + neutrons
- D) Electrons + neutrons
Q3. Isotopes of the same element differ in their number of:
- A) Protons
- B) Electrons
- C) Neutrons
- D) Ions
Q4. The bond formed by the transfer of electrons between atoms is a(n):
- A) Covalent bond
- B) Ionic bond
- C) Hydrogen bond
- D) Nonpolar bond
Q5. The elements grouped as CHNOPS are the major elements of living organisms. The "P" stands for:
- A) Potassium
- B) Phosphorus
- C) Platinum
- D) Lead
Q6. Carbon is central to life mainly because it can form:
- A) Only ionic bonds
- B) Four stable covalent bonds
- C) Hydrogen bonds only
- D) A single bond only
Q7. Water is described as a "universal solvent" because it dissolves many:
- A) Nonpolar substances
- B) Polar and ionic substances
- C) Gases only
- D) Metals only
Q8. A solution with a pH of 3 is:
- A) Basic
- B) Neutral
- C) Acidic
- D) A buffer
Q9. The upward movement of water in a thin tube against gravity is called:
- A) Cohesion
- B) Surface tension
- C) Capillary action
- D) Adhesion
Q10. A substance made of two or more elements chemically bonded in a fixed ratio is a:
- A) Mixture
- B) Compound
- C) Isotope
- D) Ion
Section B — Matching (1 mark each)
Q11–Q15. Match each term (left) to its correct description (right). Write the letter.
| # | Term | Description | |
|---|---|---|---|
| Q11 | Cohesion | A | Resistance of water surface to being broken |
| Q12 | Adhesion | B | Attraction between water molecules |
| Q13 | Surface tension | C | Substance that resists changes in pH |
| Q14 | Buffer | D | Attraction of water to other surfaces |
| Q15 | Specific heat | E | Amount of heat needed to raise temperature |
Section C — True/False WITH Justification (2 marks each)
State True or False (1 mark) AND give a one-line reason (1 mark).
Q16. A nonpolar covalent bond involves unequal sharing of electrons.
Q17. In a chemical reaction, reactants are converted into products.
Q18. Neutrons carry a positive charge equal to that of protons.
Q19. A neutral solution has a pH of 7 because [H^+] equals [OH^-].
Q20. Salt water is an example of a pure compound.
Answer keyMark scheme & solutions
Section A (10 marks)
Q1 — C) Electron (1). Electrons carry the negative charge; protons positive, neutrons neutral.
Q2 — B) Protons (1). Atomic number is defined as the proton count, which identifies the element.
Q3 — C) Neutrons (1). Isotopes share proton number but differ in neutron number, hence different mass numbers.
Q4 — B) Ionic bond (1). Ionic bonds form by electron transfer creating oppositely charged ions; covalent bonds share electrons.
Q5 — B) Phosphorus (1). CHNOPS = Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur.
Q6 — B) Four stable covalent bonds (1). Carbon has 4 valence electrons, forming diverse, stable chains/rings.
Q7 — B) Polar and ionic substances (1). Water's polarity lets it surround and dissolve charged/polar solutes.
Q8 — C) Acidic (1). pH < 7 is acidic; pH 3 has high [H^+].
Q9 — C) Capillary action (1). Combined cohesion + adhesion pulls water up narrow tubes.
Q10 — B) Compound (1). Fixed ratio + chemical bonding defines a compound (mixtures vary and are not bonded).
Section B (5 marks)
Q11 — B (1) Cohesion = water–water attraction. Q12 — D (1) Adhesion = water–other surface attraction. Q13 — A (1) Surface tension = surface resists breaking. Q14 — C (1) Buffer = resists pH change. Q15 — E (1) Specific heat = heat to raise temperature.
Section C (10 marks)
Q16 — False (1). Reason: nonpolar covalent bonds share electrons equally; unequal sharing describes polar bonds (1).
Q17 — True (1). Reason: reactants (starting substances) are transformed into products (end substances) (1).
Q18 — False (1). Reason: neutrons are electrically neutral; only protons carry positive charge (1).
Q19 — True (1). Reason: at pH 7 the concentrations of H⁺ and OH⁻ are equal, giving neutrality (1).
Q20 — False (1). Reason: salt water is a mixture (solution) of salt and water, not chemically bonded in fixed ratio (1).
Total: 30 marks
[
{"claim":"pH 3 corresponds to H+ concentration 1e-3, which is acidic (>1e-7)","code":"pH=3; H=10**(-pH); result = H > 10**(-7)"},
{"claim":"Neutral pH 7 gives H+ = OH- = 1e-7","code":"H=10**(-7); OH=10**(-14)/H; result = (H == OH)"},
{"claim":"Carbon has 4 valence electrons enabling 4 bonds","code":"valence=4; result = (valence == 4)"},
{"claim":"CHNOPS lists exactly 6 major elements","code":"elements=['C','H','N','O','P','S']; result = (len(elements) == 6)"}
]