Can we give a bipolar signal to ADC of ATmega88?
This information can be found in the datasheet.

In the ADC section it says it can measure voltages between 0&nbsp;V and Vcc. In the electrical characteristics section it says the absolute maximum for any pin except reset is -0.5&nbsp;V to Vcc + 0.5&nbsp;V.

Therefore, no it can't measure a negative voltage, and additionally, a negative voltage below -0.5&nbsp;V is not recommended.

However you can bias the input so that it is within the 0&nbsp;V to Vcc range of the ADC. For example, see the first answer to question How to read an audio signal using ATmega328?.