"In second" or "in seconds" when talking about time [closed]

When talking about time as a unit, which one is correct, in second or in seconds?

For example:

How long does it take to complete the task in second?

or

How long does it take to complete the task in seconds?

The correct form is in seconds:

Please specify the time in seconds (in minutes, in days, in years, etc).

Use the plural, "seconds".

In general, when you do not know whether the number of something is one or more than one, you use the plural.

Like, "How many people attended the meeting?", NOT "How many person attended the meeting?"

Even if the number is most likely one: "Polygamy is illegal here, but the number of wives Bob has is unknown." NOT "number of wife".