Answer : The correct option is, (b) 22.5 M
Explanation : Given,
Mass of calcium nitrate tetrahydrate = 266 g
Molar mass of calcium nitrate tetrahydrate = 236.15 g/mole
Volume of solution = 
Molarity : It is defined as the moles of solute present in one liter of solution.
Formula used :

Now put all the given values in this formula, we get:

As calcium nitrate tetrahydrate dissociate to give 1 mole of calcium ion, 2 moles of nitrate ion and 4 moles of water.
The concentration of nitrate ion = 
Thus, the concentration of nitrate ion is, 22.5 M
Counting gives an exact number and exact numbers have infinite sig figs.
Water is formed when this happens
The answer is 10-12. The relationship of pH and [H+] is pH = -lg[H+]. And the higher pH, the stronger base is. So the strongest base has the lowest concentration of H+.
The answer is likely to be A