Some Important Question for Class 10

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Some Important Question for Class 10

WORKSHEET – CLASS X (AUGUST)

Subject: Science — Answers

  1. Which reaction is used in black & white photography?

    Photolytic decomposition of silver bromide: 2AgBr ⟶ 2Ag (black) + Br2 (in light)

  2. Differentiate between displacement and double displacement reactions.

    Displacement: A + BC ⟶ AC + B (e.g., Zn + CuSO4 ⟶ ZnSO4 + Cu)
    Double displacement: AB + CD ⟶ AD + CB (e.g., AgNO3 + NaCl ⟶ AgCl + NaNO3)

  3. What happens when dilute HCl is added to iron filings?

    Hydrogen gas evolves; ferrous chloride forms: Fe + 2HCl ⟶ FeCl2 + H2↑

  4. Why is respiration considered an exothermic reaction?

    Oxidation of glucose releases energy (ATP): C–H bonds break and energy is released; hence exothermic.

  5. Mixing lead(II) nitrate and potassium iodide?

    Yellow ppt. of lead(II) iodide forms; it’s a double displacement reaction:
    Pb(NO3)2 + 2KI ⟶ PbI2↓ (yellow) + 2KNO3

  6. Balanced equations

    i) Ca(OH)2 + CO2 ⟶ CaCO3 + H2O
    ii) 2KBr + BaI2 ⟶ 2KI + BaBr2

  7. Decomposition reactions with heat / light / electricity

    Heat: CaCO3 ⟶ CaO + CO2
    Light: 2AgBr ⟶ 2Ag + Br2
    Electricity: 2H2O ⟶ 2H2 + O2

  8. Why is diffusion insufficient for multicellular organisms?

    Distances are large; diffusion is too slow. Specialized transport (blood) is required.

  9. Criteria to decide whether something is alive

    Metabolism, cellular organization, growth, reproduction, response to stimuli, and homeostasis.

  10. Essential life processes

    Nutrition, respiration, transport, excretion, control & coordination, and (for continuity) reproduction.

  11. Outside raw materials used by an organism

    Food, water, oxygen (and minerals in plants).

  12. Complete reaction of photosynthesis

    6CO2 + 12H2O ⟶ C6H12O6 + 6O2 + 6H2O (sunlight, chlorophyll)

  13. Steps involved in photosynthesis

    Light absorption → Water splitting & energy conversion → CO2 reduction to carbohydrates.

  14. Element essential for protein synthesis

    Nitrogen.

  15. Enzyme that breaks down starch to simple sugars

    Amylase (salivary amylase).

  16. Peristaltic movements

    Rhythmic contraction and relaxation of alimentary canal muscles pushing food forward.

  17. Residual volume

    Air left in lungs after maximum exhalation (≈1.2 L in adults).

  18. Numerical (Concave lens): f = −15 cm, image at 10 cm; find object distance & magnification.

    Lens formula: 1/f = 1/v − 1/u, with f = −15, v = −10 ⇒ u = −30 cm.
    Magnification: m = v/u = (−10)/(−30) = 1/3 (virtual, upright, one-third size).

  19. Numerical (Convex lens): f = 10 cm, u = −15 cm, h = 2 cm.

    1/f = 1/v − 1/u ⇒ v = 30 cm.
    m = v/u = 30/(−15) = −2 ⇒ real, inverted, twice the size; h′ = −4 cm.

  20. Where to place an object before a convex lens to get a real image of the same size?

    At 2f (twice the focal length) from the lens.

  21. A spherical mirror and a thin spherical lens each have focal length −15 cm. They are likely to be?

    Mirror: Concave mirror (negative f).   Lens: Concave (diverging) lens (negative f).

  22. No matter how far you stand, your image appears erect. The mirror is likely to be?

    Convex mirror (always erect; plane mirror also forms erect images at any distance, but for spherical mirrors this points to convex).

  23. Name the mirrors used in:

    A) Solar furnace — Concave (converging).
    B) Headlights of a car — Concave (parabolic/concave reflector).
    C) Side/rear-view mirror — Convex (wide field).

  24. Meaning of refractive index of diamond (n = 2.42)

    Light travels 2.42× slower in diamond than in vacuum; n = c/v = 2.42.

  25. Air to water: does the ray bend towards or away from the normal? Why?

    Towards the normal, because light slows down in the optically denser medium (water).

Note: Sign convention used: real is positive for distances along incident light for mirrors/lenses; for lenses, focal length is positive (convex) and negative (concave).
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