Noesis
Level 1 — RecognitionHydrogen and s-Block

Hydrogen and s-Block

printable — key stays hidden on paper

Level 1: Recognition

Time: 20 minutes | Total Marks: 25

Section A — Multiple Choice Questions

(Choose the correct option. 1 mark each)

Q1. Hydrogen resembles halogens because it: (a) has one electron only (b) needs one electron to attain noble gas configuration (c) is a metal (d) forms basic oxides

Q2. The isotope of hydrogen that is radioactive is: (a) Protium (b) Deuterium (c) Tritium (d) None

Q3. Which of the following is an interstitial (metallic) hydride? (a) NaH (b) CH₄ (c) TiH₁.₇₃ (d) H₂O

Q4. The H–O–H bond angle in water is: (a) 109.5° (b) 104.5° (c) 107° (d) 120°

Q5. Temporary hardness of water is due to: (a) chlorides of Ca and Mg (b) sulphates of Ca and Mg (c) bicarbonates of Ca and Mg (d) nitrates of Ca and Mg

Q6. The oxidation state of oxygen in H₂O₂ is: (a) −2 (b) −1 (c) 0 (d) +1

Q7. Sodium carbonate is manufactured industrially by the: (a) Haber process (b) Solvay process (c) Contact process (d) Ostwald process

Q8. Plaster of Paris is chemically: (a) CaSO₄·2H₂O (b) CaSO₄·½H₂O (c) CaSO₄ (d) CaCO₃

Q9. Lithium shows a diagonal relationship with: (a) Na (b) Be (c) Mg (d) Al

Q10. The alkali metal that imparts a lilac (violet) colour to flame is: (a) Na (b) K (c) Li (d) Cs

Section B — Matching

(2 marks each; ½ mark per correct match)

Q11. Match Column I with Column II.

Column I Column II
(i) NaOH (P) Setting of fractures
(ii) POP (Q) Antacid / baking
(iii) NaHCO₃ (R) Manufacture of soap
(iv) CaO (S) Quick lime

Q12. Match the element with its biological role.

Column I Column II
(i) Na⁺/K⁺ (P) Bones and teeth
(ii) Ca²⁺ (Q) Chlorophyll
(iii) Mg²⁺ (R) Nerve signal transmission
(iv) Ca²⁺ (blood) (S) Clotting of blood

Section C — True / False with Justification

(1 mark statement + 1 mark justification = ... marks as noted)

Q13. (2 marks) Ice floats on water because it is less dense than liquid water. (State T/F and justify.)

Q14. (1 mark) Beryllium shows anomalous behaviour and resembles aluminium. (T/F with one-line reason.)

Q15. (1 mark) D₂O is used as a coolant and moderator in nuclear reactors. (T/F with reason.)

Q16. (1 mark) Dihydrogen is prepared in the laboratory by reacting granulated zinc with dilute sulphuric acid. (T/F with reason.)

Answer keyMark scheme & solutions

Section A (1 mark each)

Q1. (b) — needs one electron to reach the He/noble-gas configuration, like halogens gaining one e⁻ to form X⁻; hydrogen forms H⁻. (1)

Q2. (c) Tritium — ³₁H has 2 neutrons, is unstable, β-emitter. (1)

Q3. (c) TiH₁.₇₃ — d/f-block metals absorb H₂ into lattice interstices, non-stoichiometric. NaH is ionic, CH₄ covalent, H₂O covalent. (1)

Q4. (b) 104.5° — bent shape from two lone pairs on O compressing the ideal tetrahedral 109.5°. (1)

Q5. (c) bicarbonates of Ca and Mg — Ca(HCO₃)₂, Mg(HCO₃)₂; removed on boiling. (1)

Q6. (b) −1 — peroxide linkage O–O; each O is −1. (1)

Q7. (b) Solvay process — ammonia-soda process. (1)

Q8. (b) CaSO₄·½H₂O — calcium sulphate hemihydrate. (1)

Q9. (c) Mg — Li–Mg diagonal relationship (similar size/charge ratio). (1)

Q10. (b) K — potassium gives lilac/violet flame. (1)

Section B (2 marks each; ½ each match)

Q11. (i)–R, (ii)–P, (iii)–Q, (iv)–S. (4 × ½ = 2)

  • NaOH → soap manufacture (saponification)
  • POP → setting bone fractures
  • NaHCO₃ → antacid/baking
  • CaO → quick lime

Q12. (i)–R, (ii)–P, (iii)–Q, (iv)–S. (4 × ½ = 2)

  • Na⁺/K⁺ → nerve impulse transmission (Na-K pump)
  • Ca²⁺ → bones and teeth
  • Mg²⁺ → chlorophyll centre
  • Ca²⁺ → blood clotting

Section C

Q13. (2 marks) True. (1) On freezing, water molecules form an open cage-like tetrahedral H-bonded structure with more empty space, so ice has lower density (~0.917 g/cm³) than water (1.00 g/cm³ at 4°C); density of ice < water ⇒ it floats. (1)

Q14. (1 mark) True — Be–Al diagonal relationship: both form covalent, amphoteric compounds (BeO/Al₂O₃), similar charge/radius ratio. (1)

Q15. (1 mark) True — heavy water D₂O slows (moderates) fast neutrons without absorbing them and removes heat. (1)

Q16. (1 mark) True — Zn + dilute H₂SO₄ → ZnSO₄ + H₂↑; standard lab preparation of dihydrogen. (1)

[
  {"claim": "Oxidation state of O in H2O2 is -1 (2*(+1)+2*x=0 => x=-1)", "code": "x = symbols('x'); sol = solve(Eq(2*1 + 2*x, 0), x); result = (sol[0] == -1)"},
  {"claim": "POP hemihydrate has 0.5 water per CaSO4", "code": "water = Rational(1,2); result = (water == Rational(1,2))"},
  {"claim": "Ice density (0.917) less than water density (1.0) so ice floats", "code": "d_ice=0.917; d_water=1.0; result = (d_ice < d_water)"},
  {"claim": "Tritium mass number 3 = 1 proton + 2 neutrons", "code": "protons=1; neutrons=2; result = (protons+neutrons == 3)"}
]