Op-amp selection for reverse polarity protection on an Arduino voltmeter
You don't need an operational-amplifier as it will add some inaccuracy due to OPAMP input bias current.
Instead, use a Schottky diode parallel to 10K resistor and ground.
If the reverse voltage is applied, the voltage across the ADC pin will be at max -0.3 to -0.5V which is safe for Arduino.