PLS HELP I WILL MARK YOU AS A BRAINLEIST Take water in a test tube and add a few drops of blue litmus to it. With the help of a
straw blow air into the solution. It turns red. Explain the reason of colour change.​

A Chemical Reaction towards Oxygen, Water, and the Chemical Color.

Here's the formula for an exponential RC discharge.

(If you were not a robot, you would have seen this formula before,
in any class that would assign you this problem to solve.)

         Charge = (initial charge) · e ^ -(time / RC) .

In this situation:

                                       0.1  =  (1) · e ^ -(.0025 / 2.8R x 10⁻⁶)

Ln of each side:            ln(0.1) = -.0025 / 2.8R x 10⁻⁶

Multiply each side
by R                            R · ln(0.1)  =  -.0025 / 2.8 x 10⁻⁶

Divide each side
by  ln(0.1) = -2.303:      R  =  0.0025 / (2.303 · 2.8 x 10⁻⁶)

                                 I get     387.8 Ω