Correct Answer: At a distance.

Solution : The correct choice is the second option .

In the context of the sentence "Being an ardent professional, the lawyer always kept his clients at an arm’s length which means to maintain a professional distance or detachment from some person.

The meanings of the other idioms are as follows:

• Away from each other: This phrase implies a separation or distance between two or more entities.
• At a distance: Similar to "away from each other," this phrase also indicates maintaining a physical or emotional separation from something.
• Under wraps: This expression means keeping something secret or concealed.
• Alert and prepared: This phrase indicates being attentive, vigilant, and ready for any situation.