Class 10 Science Competency-Based Practice

A student puts a clean zinc strip in blue copper sulfate solution.

Question 1. What happens to the strip and the solution?

Worked answer. Copper deposits on the strip and the blue fades as Cu²⁺ is consumed.

Question 2. Write the balanced equation and identify what is oxidised.

Worked answer. Zn + CuSO₄ → ZnSO₄ + Cu. Zinc loses electrons to form Zn²⁺, so zinc is oxidised.

Three solutions have pH 3, 7 and 10 and are labelled P, Q and R respectively.

Question 1. Which solution turns red litmus blue?

Worked answer. R. Its pH is above 7, so it is alkaline.

Question 2. Which solution releases carbon dioxide with sodium carbonate? Explain.

Worked answer. P. Its hydrogen ions react with carbonate ions to form water and carbon dioxide.

Three iron nails are kept separately in dry air, boiled water sealed under oil, and ordinary tap water exposed to air.

Question 1. Which nail should rust most readily?

Worked answer. The nail in tap water exposed to air has access to both water and oxygen.

Question 2. Why use an oil layer over the boiled water?

Worked answer. Boiling removes much of the dissolved oxygen. The oil limits oxygen from the air dissolving back into the water.

An alkene reacts with hydrogen over nickel to form propane.

Question 1. Identify the alkene and write the equation.

Worked answer. Propene. C₃H₆ + H₂ → C₃H₈.

Question 2. Why is the product classified as saturated?

Worked answer. All its carbon–carbon bonds are single bonds, so it has no carbon–carbon double bond for further addition.

A plant is destarched and part of one leaf is covered with opaque paper before exposure to sunlight.

Question 1. Which region turns blue-black after the iodine test?

Worked answer. The uncovered green region. Starch formed there during exposure.

Question 2. Why destarch the plant first?

Worked answer. It reduces pre-existing starch so the result reflects photosynthesis during the light treatment.

A seedling in a box with a side window grows toward the window.

Question 1. Name the response and explain the bending.

Worked answer. Positive phototropism. The shaded side of the shoot elongates faster under the influence of auxin.

Question 2. What would you expect with uniform light from directly above?

Worked answer. There should be little sideways bending attributable to light because both sides receive similar illumination.