Gas Produced by Cows and Landfill Sites
Puzzle 10 of Smelly Things Easy Pack
Question is: Gas Produced by Cows and Landfill Sites
and the answer is: METHANE
Word Meaning:
METHANE — (organic chemistry, uncountable) The simplest aliphatic hydrocarbon, CH₄, being a constituent of natural gas, and one of the most abundant greenhouse gases.
Definitions from Wiktionary.