Correct Answer: Cowards

Solution : The most appropriate meaning of the underlined idiom is the second option.

Explanation: The idiom "yellow bellies" is used to describe individuals who are cowardly or lacking courage. In the context of the sentence, when the war breaks out, those who were previously war-mongering social media activists become fearful and cowardly. The term "yellow bellies" is often used colloquially to denote individuals who lack bravery or courage in challenging situations.

So, the correct sentence would be: "When the war breaks out, all the war-mongering social media activists become cowards ."

The meanings of the other options are as follows:

• Zealots : This term refers to individuals who are fanatical or extreme in their beliefs or actions.
• Sceptics : This term refers to individuals who are sceptical or doubtful.
• Upset stomachs : This term refers to a literal expression referring to a physical condition where the stomach is uncomfortable or experiencing digestive issues.