Which of the following is a synonym for "inert"?

The term "inert" refers to something that is inactive, not moving, or not reacting. Therefore, "inactive" aligns perfectly as a synonym because it also suggests a state of not being active or not engaging in any activity.

The other options do not convey the same meaning as "inert." "Illegal" relates to the concept of something being against the law, which is entirely different from inactivity. "Unreadable" pertains to something that cannot be read or interpreted, often due to poor clarity, and does not correspond to the concept of inactivity. "Contributing" implies participation or involvement, which is the opposite of being inert. Thus, "inactive" is the most appropriate synonym for "inert."