Question

A sample of grape juice has a hydroxide ion concentration of 1.4 × 10-10 M.

Answer 1

grape juice
pOH = -log[1.4*10⁻¹⁰]≈9.6
pH=14-pOH=14-9.6=4.4

orange juce
pH= -log[1.8*10⁻⁴]=3.7

Orange juice has lower pH, so it is more acidic. 

Answer 2

The Answer on E2020 is C Acidity increases as the hydronium ion concentration increases and the pH decreases.