Two safety measures commonly used in electric circuits and appliances are:

Here are the answers to your questions:

33. Two safety measures commonly used in electric circuits and appliances are:

• Fuses or Circuit breakers to prevent overcurrent.
• Earthing or Grounding to protect against electric shock.

34. Properties of magnetic field lines:

• They originate from the North pole and end at the South pole outside the magnet.
• They form closed loops inside the magnet, from South to North pole.
• They never intersect each other.
• The tangent at any point on a field line gives the direction of the magnetic field at that point.
• The degree of closeness of the field lines indicates the strength of the magnetic field.

35. Trophic levels are the positions that organisms occupy in a food chain. Each level represents a step in the transfer of energy.

Example of a food chain: Grass $\rightarrow$ Deer $\rightarrow$ Lion

• Grass: Producers (First trophic level)
• Deer: Primary consumers (Second trophic level)
• Lion: Secondary consumers (Third trophic level)

36. Ozone ($\text{O}_3$) is a molecule composed of three oxygen atoms. In the stratosphere, it forms the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the sun. Its effect on the ecosystem is crucial: by absorbing UV radiation, it protects living organisms from skin cancer, cataracts, and damage to DNA, thus maintaining the balance of ecosystems.

37. Changes seen in boys at the time of puberty include:

• Increase in height and weight.
• Growth of facial hair (beard and mustache) and body hair.
• Deepening of the voice due to the growth of the larynx (Adam's apple).
• Enlargement of the testes and penis.
• Increased muscle development.

38. The balanced equations for the following chemical reactions are:

i) Hydrogen + Chlorine $\rightarrow$ Hydrogen Chloride

$$\text{H}_2(\text{g}) + \text{Cl}_2(\text{g}) \rightarrow 2\text{HCl}(\text{g})$$

ii) Calcium hydroxide + Carbon dioxide $\rightarrow$ Calcium carbonate + Water

$$\text{Ca(OH)}_2(\text{aq}) + \text{CO}_2(\text{g}) \rightarrow \text{CaCO}_3(\text{s}) + \text{H}_2\text{O}(\text{l})$$

iii) Sodium + Water $\rightarrow$ Sodium hydroxide + Hydrogen

$$2\text{Na}(\text{s}) + 2\text{H}_2\text{O}(\text{l}) \rightarrow 2\text{NaOH}(\text{aq}) + \text{H}_2(\text{g})$$

39. Physical properties of metals:

• They are generally lustrous (shiny).
• They are malleable (can be hammered into thin sheets).
• They are ductile (can be drawn into thin wires).
• They are good conductors of heat and electricity.
• They are typically solids at room temperature (except mercury).
• They have high melting and boiling points.

40. Corrosion is the process by which metals are gradually eaten away by the action of air, moisture, or a chemical (like an acid) on their surface. A common example is the rusting of iron. Some remedies to prevent corrosion include:

• Painting the metal surface.
• Oiling or greasing the metal surface.
• Galvanizing (coating with a layer of zinc).
• Electroplating (coating with a layer of another metal like chromium or nickel).
• Alloying (mixing metals to create a more resistant material, e.g., stainless steel).

41. The hormones and their functions secreted by the given endocrine glands are:

i) Pancreas:

• Hormones: Insulin and Glucagon.
• Functions: Insulin lowers blood glucose levels by promoting glucose uptake by cells. Glucagon raises blood glucose levels by stimulating the liver to release stored glucose.

ii) Thyroid gland:

• Hormone: Thyroxine.
• Functions: Regulates the body's metabolism, growth, and development.

iii) Ovaries:

• Hormones: Estrogen and Progesterone.
• Functions: Estrogen is responsible for the development of female secondary sexual characteristics and regulates the menstrual cycle. Progesterone helps in maintaining pregnancy.