Final answer:
The verb 'were' in the sentence is in the subjunctive mood, which is used for wishes, suggestions, or hypothetical situations.
Step-by-step explanation:
The mood of the verb in the sentence "If Tom were more thrifty, he would be richer" is the subjunctive mood. In English grammar, the subjunctive mood is used to express wishes, suggestions, requirements, or to state hypothetical or unlikely scenarios. The verb 'were' in this case is not used to indicate a fact or opinion, as with the indicative mood, nor is it giving a command like the imperative mood. Instead, it introduces a hypothetical condition that is not currently true about Tom; it talks about a situation that would be possible if conditions were different. Thus, the subjunctive mood is the correct answer in this context.
The subjunctive mood is used to express hypothetical or unlikely situations, wishes, suggestions, or requirements. In this sentence, the use of 'were' indicates a hypothetical situation where Tom is not currently thrifty, but if he were, he would be richer.