Which of the following is a pure substance? diamond granite (quartz, feldspar and mica) air

A pure substance is something that is composed of molecules or atoms of only one kind. A diamond is a pure substance for example and so is air. So if it is made of sifferent things, aka a compound, then no it is not.

there are two significant figures.

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