(c) $Molarity\ of\ base = \frac{Normality}{Acidity} = \frac{0.1}{1} = 0.1$ $M_{1}V_{1} = M_{2}V_{2}$ $0.1 \times 19.85 = M_{2} \times 20$ $M_{2} = 0.09925 \approx 0.099$
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Ph.D. in Physics with 19+ years of teaching experience.