Cesium. For non-transition elements such as rubidium, cesium, and strontium, the most chemically similar element to any other element is always one in the same column of the Periodic Table but in an adjacent row. Since strontium is not in the same column as rubidium but cesium is in the same column and an adjacent row, the answer follows. (This rule is sometimes true also for transition elements, but not always: For example, for elements in columns 8, 9, and 10, the most nearly chemically similar element is one in the same row and an adjacent column within this group, rather than one in the same column but an adjacent row.)
Strontium would be expected to be more similar to calcium due to it being in the same column of the Periodic Table, this corresponds to the amount of valance electrons, and is a comparable relationship to the similarities between lithium and sodium.
Strontium would share many similar properties with those of calcium. This is because strontium and calcium are both found within the same group, in this case, group 2 which is the alkaline earth metals.
Strontium is more similar to Calcium then Rubidium as they are both in the same group (vertical). Where as Rubidium is in the same period but don't share similar properties (horizontal).
Strontium is most similar to calcium as they are both group 2a elements.
Strontium is closer to potassium because both are metals and belong to s-block of periodic table.
Strontium and potassium are metals, bromine is a nonmetal.
Ba
Strontium is chemically very similar to Calcium. The human body will readily use Strontium as bone-making material, but Strontium does not satisfy the other uses the human body has for Calcium e.g. regulating calcium content in blood, etc.
They have "ium" in their name.
Magnesium
because they are all alkaline earth metals and occur naturally in nature.
This element is strontium (Sr).
Strontium is chemically very similar to Calcium. The human body will readily use Strontium as bone-making material, but Strontium does not satisfy the other uses the human body has for Calcium e.g. regulating calcium content in blood, etc.
Calcium, rubidium, lithium and strontium have red (or similar) colors in the flame tast.
Cesium. For non-transition elements such as rubidium, cesium, and strontium, the most chemically similar element to any other element is always one in the same column of the periodic table but in an adjacent row. Since strontium is not in the same column as rubidium but cesium is in the same column and an adjacent row, the answer follows. (This rule is sometimes true also for transition elements, but not always: For example, for elements in columns 8, 9, and 10, the most nearly chemically similar element is one in the same row and an adjacent column within this group, rather than one in the same column but an adjacent row.)
They have "ium" in their name.
Calcium shares properties with Magnesium and Strontium.
The chemical properties of calcium are most similar to (in between) the chemical properties of magnesium and strontium.
Magnesium
because they are all alkaline earth metals and occur naturally in nature.
This element is strontium (Sr).
Rubidium (Rb) can react with many things such as hydrogen because rubidium has one spare electron 2, 8, 18, 8, 1 and hydrogen has only one outer electron so hydrogen in water will reactvigorously with rubidium as hydrogen is desperate to gain one electron and rubidium is desperate to lose one electron and when these bond they form an ion.
Calcium is in group 2/IIA, so the other elements in that group would be expected to behave most like calcium.
To know which pairs of ions produce similar colors in the flame test it is important to know what the pairs of ions are. Without knowing this a person will not be able to know which would produce similar colors in the test.