. What is the relation between nanosecond and second

A nanosecond is one billionth of a second. Seconds. A second is the base unit of time. Originally, it was based on the length of the day.1 sec = 10^9 nano seconds

one thousand-millionth of a second.
A nanosecond is an SI unit of time equal to one thousand-millionth of a second, that is, ¹/1 000 000 000 of a second, or 10−9 seconds. The term combines the prefix nano- with the basic unit for one-sixtieth of a minute.