Compounds containing chlorine have long been used to disinfect the water in swimming pools, but in recent years a compound of a less corrosive halogen has become a popular alternative disinfectant. What is the name of this fourth-row element

Explanation:

A period 4 element is one of the chemical elements in the fourth row (or period) of the periodic table of the elements.

...

Period 4 element.

HydrogenRubidium

Strontium

Yttrium

Zirconium

Niobium

increased stability in the completion of fluorine's outer shell.

the dissociation of nickel hydroxide is follows:

the concentration of hydroxide ion is

the equilibrium constant value of nickel hydroxide is = 6.1 * 10^-^1^6 and thus equilibrium equation can be written as:

thus, concentration of ni is 0.23 * 10^-^4 mol /l