Q1. What are decomposition reactions? Explain with the help of a balanced chemical equation. (2 marks)
Q2. Draw the structure of a nephron and label the following on it- Glomerulus, Bowman’s capsule, Renal artery and Collecting duct. (2 marks)
Q3. What happens when zinc metal reacts with sulphuric acid? Write the chemical equation involved in this reaction. (2 marks)
Q4. Draw ray diagrams showing the image formation by a convex lens when an object is placed (2 marks)
(a) between optical centre and focus of the lens
(b) between focus and twice the focal length of the lens
Q5. Sunita and her mother had an appointment with an optician. Optician prescribed corrective lenses to Sunita having a power equal to + 5.0 D. The lens prescribed to
her mother has power equal to – 2.5 D. (3 marks)
(a) What is the focal length of the lens prescribed to Sunita?
(b) Which type of spherical lens is prescribed to Sunita’s mother?
(c) What is the power of the combination of the two lenses (if placed in contact), prescribed to Sunita and her mother?
Q6. Give the reason for the following: (3 marks)
(a) The taste and smell of chips change when the packet is left open for a few days.
(b) Magnesium ribbon is cleaned before burning in air.
(c) Iron articles get coated with reddish brown powder when left for sometime.
Q7. (a) Why do arteries have thick and elastic walls while veins have thin walls? (2 marks)
(b) What is the role of valves in the heart? (1 mark)

A decomposition reaction is a type of reaction in which one reactant breaks down into two or more products. This can be represented by the general equation: H2O2 → 2H + 2O. In this example the breakdown of hydrogen peroxide occurs and water and oxygen are formed.

What happens when zinc metal reacts with sulphuric acid?

Zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen This hydrogen goes up into the atmosphere whereas the zinc sulphate remains.

Why should a magnesium ribbon be cleaned before burning in air?

Magnesium ribbon should be cleaned before burning in air because Magnesium metal combines with oxygen to form Magnesium Oxide (MgO) layer, which is a very stable molecule.

Why arteries have thick, elastic walls, while veins have thin walls?

Arteries have thick, elastic walls, while veins have thin walls because arteries are under more pressure, as compared to veins that are under less pressure. Arteries are big in size whereas veins are small.

What is the role of valves in the heart?

The role of valves in the heart is that these valves prevent the backward flow of blood.

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