The question is b) and the first mark that I got was that radiation flux of Mars is less than half that of Earth’s.
O.K. The question is really asking you to understand that the flux arriving at Earth is an average and varies considerably according to season, cloud cover, ocean depth etc. It wants you to compare the flux arriving at Earth (we know Earth supports life) with that arriving at Mars.
So you have to make an intelligent estimate by comparing the range of flux arriving at different places on earth, (where we know life is supported) with that average flux arriving at Mars.
For instance, we know life exists in the oceans where the flux is attenuated significantly with depth. The average flux arriving in the deep ocean supports life but is still well below the average flux arriving at say, the equator, on Mars. So from an energy perspective when compared with the Earth, if there is water on Mars, then the radiation flux arriving at Mars at shallow depth, should also be capable of supporting life.