From the given options, choose the word closest in meaning to "Vacuous"

Expressionless

The word that is closest in meaning to "vacuous" is expressionless.

• Vacuous means lacking in intelligence or serious thought; lacking meaning, importance, or substance.
• Expressionless means not showing or expressing any emotion or feeling.

The other options have different meanings.

• Intelligent means having or showing a high degree of intelligence or mental acuteness.
• Meaningful means having a meaning or purpose.
• Thinking means using one's mind to consider or reason about something.

So, the answer is Option 2: Expressionless.