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Many pure metals like copper… (Class 10 Science 2025, Q37)

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ScienceCBSE Class 10 · Board exam 2025, set 31/6/1 · 4 marks · Case-based

CBSE Class 10 Science 2025: question 37

Set in the CBSE Class 10 board exam of 2025, paper 31/6/1, section E, question 37, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q37 · 4 marks · Case-basedCompetency-basedMetals and Non-metals

Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns etc. are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.

  1. (I)

    How does electrical conductivity and melting point of a metal change when it is converted to its alloy by mixing a small amount of an element in it ?

    1 mark
  2. (II)

    Name an alloy used for welding two wires together in an electric circuit. Write its major constituents.

    1 mark
  3. (III)(a)

    What are alloys ? How is 'Brass' (an alloy) prepared ?

    2 marks

  4. OR

    (III)(b)

    What is stainless steel ? How is it prepared ? Write one important property which makes it more useful in making cooking utensils as compared to its primary metal.

    2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/6/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Compare how easily a fuse wire alloy melts with how easily the pure metals melt.

Hint 2

Welding of wires needs an alloy with a low melting point. Recall which two metals give that.

Hint 3

For the alloys, recall their compositions from the NCERT list: brass = Cu + ?, stainless steel = Fe + ? + ?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (I) When a pure metal is converted into its alloy, its electrical conductivity decreases and its melting point (generally) decreases, compared with the pure metal.

    1 mark

  2. (II) The alloy used for welding (joining) electrical wires is solder.

    ½ mark

  3. (II) Its major constituents are lead (Pb) and tin (Sn).

    ½ mark

  4. (III)(a) An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal.

    1 mark

  5. (III)(a) Brass is prepared by melting copper and adding zinc to it in a definite proportion. The molten mixture is then cooled to room temperature.

    1 mark

  6. (III)(b) Stainless steel is an alloy of iron with chromium and nickel (and a small amount of carbon).

    1 mark

  7. (III)(b) Preparation: iron is first mixed with a very small amount of carbon (about 0.05%) to make it hard and strong. This steel is then melted and mixed with nickel and chromium in definite proportions, and cooled.

    ½ mark

  8. (III)(b) Property: stainless steel does not rust (it resists corrosion), unlike pure iron. This makes it better for cooking utensils.

    ½ mark

Answer: (I) Conductivity and melting point both decrease. (II) Solder: lead and tin. (III)(a) An alloy is a homogeneous mixture of metals (or a metal and a non-metal); brass is made by melting copper with zinc. (III)(b) Stainless steel is iron + Cr + Ni (+ a little C), made by melting iron with carbon and then with Ni and Cr; it does not rust.

Where the marks are

  • (I) Both conductivity and melting point decrease (1 mark)
  • (II) Names solder (½ mark) and gives lead and tin as constituents (½ mark)
  • (III)(a) Definition of alloy (1 mark); brass from copper and zinc in definite proportion (1 mark)
  • (III)(b) Composition of stainless steel (1 mark); method of preparation (½ mark); does not rust (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Metals and Non-metals, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/6/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.