Using this formula..
pH = -log(H^+)
find the pH
1.6 x 10^(-5)
You need to learn how to do this.
Punch 1.6 x 10^-5 into your calculator.
Hit the log button. You should get -4.79588 so the equation now looks like this.
pH = -log(H^+)
pH = -log(1.6 x 10^-5)
pH = -(-4.79588)
pH = 4.79588 which rounds to
pH = 4.80