A certain element is represented as X¹²6.

Here are the solutions to the questions:

44. A certain element is represented as $X^{12}_{6}$. a) The number of protons is the atomic number, which is the subscript. Number of protons = $\boxed{\text{6}}$ b) The mass number is the superscript. Mass number = $\boxed{\text{12}}$

45. An atom of an element has an electron arrangement of 2.8.1 a) The total number of electrons is $2 + 8 + 1 = 11$. In a neutral atom, the number of protons equals the number of electrons. The element with atomic number 11 is Sodium (Na). b) The atom has $\boxed{\text{11 electrons}}$.

46. Name any two metals and non-metals: Metals: i) Iron ii) Copper Non-metals: i) Oxygen ii) Carbon

47. An element has 20 protons. An element with 20 protons has an atomic number of 20. This element is Calcium (Ca). Calcium is located in Group 2 of the periodic table, which consists of alkaline earth metals. The element is a $\boxed{\text{metal}}$.

48. Identify the element whose atomic structure is illustrated below. (The illustration of the atomic structure is missing from the provided image, so the element cannot be identified.)

49. We can use the following to classify elements as either metallic or non-metallic:

    • Their physical properties such as electrical conductivity, thermal conductivity, malleability, ductility, luster, and state at room temperature.
    • Their chemical properties, particularly their tendency to lose (metals) or gain (non-metals) electrons to form ions.
    • Their position on the periodic table.

50. Different elements are important to us in different ways. Some of their importance includes:

    • Oxygen is essential for respiration in living organisms and for combustion.
    • Iron is used in construction and is a vital component of hemoglobin in blood.
    • Calcium is crucial for strong bones and teeth, and is used in building materials like cement.
    • Carbon forms the basis of all organic life and is used in fuels and materials like graphite and diamonds.

51. Two uses of phosphorus are:

    • It is a key component in fertilizers to promote plant growth.
    • It is used in the manufacturing of matches and fireworks.

52. Grade 8 learners will be preparing oxygen gas in the laboratory. They would require the following for the practical activity:

    • Chemicals: Hydrogen peroxide ($H_2O_2$) and Manganese(IV) oxide ($MnO_2$) as a catalyst.
    • Apparatus: Test tube or conical flask, delivery tube, gas jar, trough of water (for collection by downward displacement), retort stand and clamp, and a stopper.