Select the option that expresses the opposite meaning of the underlined word.

The explosive used is of my own formulation and I can vouch for its efficiency.

The correct answer is invalidate.

Step-by-step Explanation:

1. Analyze the underlined word in context:
In the sentence, "The explosive used is of my own formulation and I can vouch for its efficiency," the word vouch means to assert, confirm, guarantee, or attest to the truth, accuracy, or effectiveness of something based on one's own experience or knowledge.

2. Identify the opposite meaning:
Since "vouch" means to confirm, support, or certify the validity of something, its opposite must mean to make something invalid, disprove, deny, or take away its support or authority.

3. Evaluate the options:

• invalidate: To make logical arguments or official statements invalid, to disprove, or to nullify. This is the direct opposite of vouching for or confirming something's validity.
• maintain: To assert or keep in existence. This is close to the meaning of supporting or vouching, not the opposite.
• witness: To see or provide evidence for something. This is related to vouching (as a witness attests to things), not the opposite.
• certify: To formally declare or confirm something is true. This is a synonym of vouch, not the opposite.

Therefore, invalidate is the correct option that expresses the opposite meaning of vouch.