A student represented an atom of element J using the diagram below.

Here are the solutions to the questions:

8. A student represented an atom of element J using the diagram below.

b) Write the valency of element J and the oxidation number of its ion.

• From the diagram, element J has an electron configuration of 2, 8, 6. To achieve a stable octet, it needs to gain 2 electrons.
• Valency: 2
• Oxidation number of its ion: -2

9. When the oxide of metal D is heated in the presence of metal S, the oxide is reduced. The oxide of metal S is not reduced when heated together with metal E and with metal D. The oxide of metal E is reduced by metal S and not by metal D. Arrange the three metals horizontally, in their order of decreasing reactivity.

Let's deduce the reactivity order:

• "The oxide of metal D is heated in the presence of metal S, the oxide is reduced." This means metal S is more reactive than metal D. ($\text{S} > \text{D}$)
• "The oxide of metal S is not reduced when heated together with metal E and with metal D." This means metal S is more reactive than both metal E and metal D. ($\text{S} > \text{E}$ and $\text{S} > \text{D}$)
• "The oxide of metal E is reduced by metal S and not by metal D." This confirms $\text{S} > \text{E}$. It also means metal D is not reactive enough to reduce the oxide of E, so metal E is more reactive than metal D. ($\text{E} > \text{D}$)

Combining these, the order of decreasing reactivity is:
S > E > D

10. Calculate the number of nitrogen atoms that are found in 1.4g of nitrogen gas (N = 14, L = 6.023 x 10^23)