Correct Answer: Option D

Explanation

You can apply any of the two methods below:

METHOD 1: The use of the solubility formula, which is;

                   Solubility = \(\frac{mass}{Molar mass}\) X \(\frac{1000}{Volume of Solvent}\)

But Molar mass of KOH = 39 + 16 + 1 = 56g/mol

Also given; mass of KOH = 28g

Volume of Solvent used = 100cm\(^3\)

Solubility = \(\frac{28}{56}\) X \(\frac{1000}{100}\)

               = 5 moldm\(^{-3}\)

METHOD 2: Using the simple proportion method

If        28g of KOH was dissolved in 100cm\(^3\) of water

then,  Xg of KOH will be dissolved in 1000cm\(^3\) of water

  X = \(\frac{{28}\times{1000}}{100}\)

  X = 280 gdm\(^{-3}\)

Recall that Molar Concentration (mol dm\(^{-3}\)) = \(\frac{Mass Concentration}{Molar mass}\)

                                                                              = \(\frac{280}{56}\)

                                                                              = 5 moldm\(^{-3}\)

Kindly choose any of the methods you find easier and comprehending.

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