To solve this question, the user needs to have knowledge about the planets in our solar system and the greenhouse effect.

Out of the given options, the planet with a poisonous atmosphere that has been described as the product of a runaway greenhouse effect is Venus.

Option A (Earth) is incorrect because while Earth is experiencing the greenhouse effect, it is not a runaway greenhouse effect. Moreover, Earth's atmosphere is not poisonous.

Option B (Mars) is incorrect because Mars does not have a poisonous atmosphere and does not currently have a significant greenhouse effect.

Option C (Venus) is correct. Venus has a thick, toxic atmosphere consisting mainly of carbon dioxide. The atmosphere is the result of a runaway greenhouse effect, which occurred when the planet's oceans evaporated and the water vapor combined with other gases in the atmosphere to trap heat. This led to a significant increase in temperature, making the planet's surface inhospitable to life.

Option D (Jupiter) is incorrect because Jupiter is a gas giant planet and does not have a solid surface or a greenhouse effect.

Therefore, the answer is: C. Venus