H2C2O4, also written as (COOH)2, is Ethandioic acid, and, as evident by the name, is an acid, and not a base
Ca(OH)2 and KOH, Calcium Hydroxide and Potassium Hydroxide, respectively, are bases when dissolved in water, as they are able to release OH- ions.
Hydrogen Iodide, HI, when dissolved in water, is a strong acid. So, that is also not a base.
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This is asking for the absolute humidity. So if the relative humidity is 65 % and the air temperature is 30 then we need to have in mind the barometric pressure which will be 760. The humidity in the air will be 0.020 kg/m3. In order to know this we calculate it eith the mass of water vapour in a unit volume of air. This is a measure of the actual water vapour content of the air. the for mula would go like this: AH = Mv / V.
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
