Which of the following is used for determining the value of 1 ampere.

The correct option is A = 1C/s.

Step 1: Understand the definition of electric current
Electric current is defined as the rate of flow of electric charge per unit time. The relationship between electric charge ($Q$), current ($I$), and time ($t$) is given by the formula:

$I=\frac{Q}{t}$

Step 2: Substitute the standard SI units
The SI unit of electric current ($I$) is the Ampere (A), the SI unit of charge ($Q$) is the Coulomb (C), and the SI unit of time ($t$) is the second (s).

Step 3: Determine the value of 1 Ampere
One Ampere is defined as the amount of electric current produced when one Coulomb of charge flows through a conductor in one second:

$1\text{A}=\frac{1\text{C}}{1\text{s}}$

Therefore, the expression used to determine 1 ampere is A = 1C/s.