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HBSE Class 11 Chemistry Half Yearly Question Paper 2024 Answer Key
Instructions :
• All questions are compulsory.
• Questions (1-9) carry 1 mark each.
• Questions (10-12) carry 2 marks each.
• Questions (13-14) carry 3 marks each.
• Question (15) case study, carry 4 marks.
• Questions (16-17) carry 5 marks each.
1. The electron affinity for the inert gases is :
(a) Zero
(b) High
(c) Negative
(d) Positive
Answer – (a) Zero
2. For the process to occur under adiabatic conditions, the correct condition is :
(a) ∆T = 0
(b) ∆P = 0
(c) q = 0
(d) w = 0
Answer – (c) q = 0
3. How many unpaired electrons are present in a Nitrogen atom?
(a) 1
(b) 2
(c) 3
(d) 4
Answer – (c) 3
4. What is the molar mass of H2O in gm/mol?
(a) 44
(b) 18
(c) 17
(d) 60
Answer – (b) 18
H2O = 2×1 + 16 = 2 + 16 = 18
5. The correct value of Avogadro’s constant will be ………….
Answer : 6.022 × 1023
6. Mathematical statement of the first law of thermodynamics is …………
Answer : ∆U = q + w
7. What is the value for the compressibility factor for ideal gas?
Answer : Z = 1
8. Name the type of system in which neither matter nor energy is exchanged with surroundings.
Answer – Isolated system
9. Assertion (A) : Graphite is an Element.
Reason (R) : Element is the pure form of substance containing the same kind of atoms.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true and (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer – (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
10. What is the oxidation number of Cl in KClO3.
Answer : Let oxidation number of Cl is x,
+ 1 + x + 3(–2) = 0
1 + x – 6 = 0
x = 5
11. Write Electronic Configuration of chromium atom.
Answer : 1s2 2s2 2p6 3s2 3p6 3d5 4s1
12. What is the reason that the first lonization energy of Nitrogen is higher while that of oxygen is lower?
Answer – Because nitrogen is more stable due to its half-filled electronic configuration.
13. Compare relative stability of the following species and indicate their magnetic properties on the basis of Molecular Orbital Theory : O2, O2+, O2–
Answer – Bond order of O2+ is 2.5, bond order of O2 is 2, bond order of O2– is 1.5.
Order of the stability is O2+ > O2 > O2–
14. A measured temperature on the Farenheit scale is 200°F. What will this reading be on Celsius?
Answer – Relationship between Fahrenheit scale and Celsius scale is given by :
F = 9/5 C + 32
C = 5/9 × (F – 32)
C = 5/9 × (200 – 32)
C = 5/9 × 168 = 93.3
Thus, the temperature is 93.3°C
15. CASE STUDY : Modern periodic table arranges the elements in the increasing order of atomic number. It has 18 groups and 7 periods. Atomic numbers are consecutive in a period and increases in the group in a pattern. Elements are divided into four blocks, s-block, p-block, d-block, and f-block based on their electronic configuration. 78% of elements are metals, about 20 elements are non-metals, and few elements like B, Si, Ge, As are metalloids. Metallic character increases down the group but decreases along the period from left to right. The physical and chemical properties vary periodically with their atomic numbers. Periodic trends are observed in atomic size, ionization enthalpies, electron gain enthalpies, electronegativity, and valence. Oxides of metals are basic, some are amphoteric. Non-metals form acidic oxides, some form neutral oxides. s-block elements are soft, highly reactive, do not show variable oxidation states. p-block elements are metals, non-metals as well as metalloids, show variable oxidation states, exist as solids, liquids, and gases. d-block elements are metals, form coloured ions, show variable oxidation states, have high melting and boiling points. Lanthanoids and actinoids are f-block elements, form coloured ions. All actinoids are radioactive.
Questions :
(a) Name the elements which belong to the d-block but are not transition metals.
Answer – Zn, Cd, Hg
(b) What are representative elements?
Answer – s-block and p-block elements are called representative elements.
(c) Which group elements are most electropositive and why?
Answer – Group 1 due to the largest atomic size and lowest ionization enthalpies in respective periods.
(d) What happens to reactivity, if you move down the group 17?
Answer – Reactivity will decrease when moving down the group 17.
16. Although CO2 and H2O are triatomic molecules the shape of H2O molecule is bent while that of CO2 is linear, explain on the basis of dipole moment.
Answer – The difference in dipole moments between H2O and CO2 is responsible for their different molecular shapes. The presence of non-bonding electron pairs in H2O leads to an uneven distribution of charge, resulting in a bent shape with a net dipole moment. Meanwhile, the symmetrical arrangement of polar bonds in CO2 leads to a linear shape with no net dipole moment.
17. What is the number of photons of light with wavelength 4000 Pm which provide 1 Joule of energy?
Answer – Energy of a photon having wavelength (λ) is given by the expression, E = hc/λ
h = Planck’s constant = 6.626 × 10–34 Js
s = speed of light = 3 × 108 m/s
λ = wavelength = 4000 Pm = 4000 × 10–12 m = 4 × 10–9 m
E = hc/λ = (6.626×10–34 × 3×108) / (4×10–9) = 4.97 × 10–17 J
Number of photons providing 1 joule of energy,
n = 1/E = 1/(4.97×10–17) = 2.01 × 1016 photons