Asample of grape juice has a hydroxide ion concentration of 1.4 × 10-10 m. which of these equations will you use to find the hydronium ion concentration?

The choices are not given, however, the question can still be solved.

We know that:
pH + pOH = 14
Converting the above equation to concentration form, we will get:
[H₃O+] * [OH-] = 10⁻¹⁴

We are given that:
concentration of hydroxide ion [OH-] = 1.4 * 10⁻¹⁰ M

Substitute with this in the above equation to get concentration of hydronium ion as follows:
[H₃O+] * [OH-] = 10⁻¹⁴
[H₃O+] * [1.4 * 10⁻¹⁰ ] = 10⁻¹⁴
[H₃O+] = 
[H₃O+] = 7.1428 * 10⁻⁵ M

Hope this helps :)

With a continuous thought process.