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CBSE Class 10 Science — practice by topic

Browse 1,188 questions across 12 Science topics. Choose what you want to revise, then open a question to check its answer and worked solution.

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Science topics

Refraction of Light and Lenses (227)Effects of Electric Current (163)Chemical Reactions and Equations (144)Life Processes in Living Organisms Part 2 (129)Life Processes in Living Organisms Part 1 (103)Metals and Non-metals (91)Environmental & Disaster Management (81)Acids, Bases and Salts (50)Carbon Compounds (50)Cell Biology and Animal Classification (50)Heredity and Evolution (50)Periodic Classification of Elements (50)

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Heating copper nitrate crystals produces black copper oxide, reddish-brown nitrogen dioxide, and oxygen. This reaction is best classified asRead the answer and worked solution →Which of the following arrangements is in correct order of increasing electronegativity (Pauling scale)?Read the answer and worked solution →The element with electronic configuration $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3$ belongs to which group and period?Read the answer and worked solution →In humans, which chamber of the heart pumps oxygenated blood to the entire body?Read the answer and worked solution →

Worked practice questions

Heating copper nitrate crystals produces black copper oxide, reddish-brown nitrogen dioxide, and oxygen. This reaction is best classified as

  1. combination
  2. displacement
  3. thermal decomposition
  4. neutralization
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Correct answer: C. thermal decomposition

A single compound, copper nitrate, breaks down into simpler substances on heating. Since heat causes the breakdown, it is a thermal decomposition reaction.

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Which of the following arrangements is in correct order of increasing electronegativity (Pauling scale)?

  1. F < O < N < C
  2. N < C < O < F
  3. C < N < O < F
  4. O < F < N < C
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Correct answer: C. C < N < O < F

Electronegativity increases across a period and decreases down a group. The Pauling-scale values for period 2 nonmetals: - C: 2.55 - N: 3.04 - O: 3.44 - F: 3.98 (highest of any element) So the correct ascending order is **C < N < O < F**. Option A reverses everything. Option C breaks the trend by putting F before O. Memory aid: "FONClBrISCHP" is the electronegativity ladder from highest to lowest among common nonmetals (F first, P last among this set).

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The element with electronic configuration $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3$ belongs to which group and period?

  1. Group 13, Period 3
  2. Group 15, Period 4
  3. Group 2, Period 4
  4. Group 17, Period 4
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Correct answer: B. Group 15, Period 4

**Period** equals the highest principal quantum number, which is 4 here. So Period 4. **Group**: the outermost shell ($n=4$) has $4s^2 4p^3$. For p-block elements, group number = 10 + (number of $s$ valence + number of $p$ valence) = 10 + (2 + 3) = **15**. This configuration matches **arsenic (As)**, atomic number 33. Check: As is below P and N in group 15 (nitrogen family), period 4. ✓

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