Learn Hardcore Japanese: gakusei ha sensei ni situmon wo simasu.

は is the topic particle. It tells us that 学生 (“the student”) is what the rest of the sentence is about. In English we might translate it as “As for the student, …” or simply drop it since English doesn’t have a direct equivalent.

Why is 先生 followed by に?

に marks the indirect object or the recipient of an action. Here it shows that 先生 (“teacher”) is the person to whom the question is being asked—literally “to the teacher.”

Why is 質問 followed by を?

を marks the direct object of the verb. Since 質問 (“question”) is what is being “done” by the student (i.e. “ask a question”), を indicates that 質問 is the thing acted upon by します.

What kind of verb is します, and why is it used with 質問?

します is the polite present form of する, the irregular “to do” verb. Japanese often forms verbs by combining a noun with する. So 質問をする literally means “to do a question,” i.e. “to ask a question.” In polite speech it becomes 質問をします.

Why is the verb します at the end of the sentence?

Standard Japanese word order is Subject-Object-Verb (SOV). You first introduce the topic (学生は), then any indirect object (先生に), then the direct object (質問を), and finally the verb (します). This is the normal sentence structure in Japanese.

Could we say 質問します instead of 質問をします? Are they the same?

Yes. In everyday speech and writing you often drop the を and simply say 質問します. It’s understood as the same compound verb (“to ask a question”). Formally you can use either, but dropping を is very common with these “noun + する” verbs.

Can we use 先生に聞きます instead of 先生に質問をします?

You can. 聞きます (from 聞く) means “to ask” or “to listen.” 先生に聞きます is more casual and means “ask the teacher.” 質問をします is a bit more formal/literal (“make a question to the teacher”). Nuance: 質問する focuses on the act of questioning; 聞く focuses on seeking information or listening.

Why not use が instead of は for 学生?

が marks the grammatical subject, often introducing new or specific information. は marks the topic or what you’re talking about. If you said 学生が先生に質問をします, you’d be emphasizing “It’s the student (and not someone else) who asks the teacher a question.” Using は simply sets 学生 as the context for the rest of the statement.