Major species present when dissolved in water Iron(ii) sulfate

Major species in the solution present in higher concentrations about more than 10% of the other species in the solution. The nature of solute that is dissolved in the solution, or the extent of reaction of different groups with the solvent decide the major species present in the solution.

Explanation:

For weak acids(bases) dissolved in water, the major species will be the undissociated acid(base) and water as the extent of dissociation of the molecular weak acid(weak base) is relatively less. For ionic solutes, the major species after dissolution in water will be the ions that form in the solution in addition to water.

Read more on - link

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.