I remember reading a short story about three robots sent as ambassadors to (I think) Mars. It was an attempt by Earth to prevent a Martian invasion or war.
The robots arrived in a spaceship designed for them - no defence from lack of atmosphere etc, which confused the Martians. However, the Martians were quite arrogant and felt they were still superior. The Martians assume that the robots are earthlings and their arrogant behaviour towards the robots prevents them from explaining they are mistaken. The Martians remain dismissive of earthlings and provide a guided tour of Mars in order to display their superiority. On the tour, one of the robots enters an acid lake (out of curiosity) and reappears unharmed, carrying the dead body of one of the most feared creatures on the planet. The robots are apologetic for the accidental death of the creature, but by now the Martians are subdued. They rethink their plans to invade Earth, thinking that all earthlings are like the robots.
Cannot remember the title or who it was by. Can anyone help?