BECE Science 2023 Paper

Concept:Elements in the same period are located in the same horizontal row of the periodic table.Explanation:Check the period of each element based on its electron shell or position in the periodic table.$\mathrm{B}$ and $\mathrm{Al}$: $\mathrm{B}$ is in period 2, while $\mathrm{Al}$ is in period 3.So they are not in the same period.$\mathrm{H}$ and $\mathrm{Li}$: $\mathrm{H}$ is in period 1, while $\mathrm{Li}$ is in period 2.So they are not in the same period.$\mathrm{Be}$ and $\mathrm{B}$: Both $\mathrm{Be}$ and $\mathrm{B}$ are in period 2.So they are in the same period.$\mathrm{Na}$ and $\mathrm{K}$: $\mathrm{Na}$ is in period 3, while $\mathrm{K}$ is in period 4.So they are not in the same period.Only the pair $\mathrm{Be}$ and $\mathrm{B}$ lies in the same horizontal row.Answer:C. $\mathrm{Be}$ and $\mathrm{B}$