**Collision Flux and Sticking Coefficient**

The collision flux of a monoatomic gas on a copper surface refers to the number of collisions that occur between gas atoms and the copper surface per unit area per unit time. In this case, the collision flux is given as 3.0*10^18 /m2 s1.

The sticking coefficient, on the other hand, represents the probability that a gas atom will stick to the surface after a collision. In this case, the sticking coefficient is given as 1.0, which means that all gas atoms that collide with the copper surface will stick to it.

**Calculating the Time Taken to Form a Complete Monolayer**

To calculate the time taken by the gas to form a complete monolayer on the surface, we need to consider the collision flux and the lattice constant of the copper surface.

1. Calculate the surface area of one copper atom:
- The lattice constant of the copper surface is given as 210 pm.
- Convert the lattice constant to meters: 210 pm = 210 * 10^-12 m.
- Since the copper surface forms a square lattice, the surface area of one copper atom is given as (210 * 10^-12 m) * (210 * 10^-12 m) = 4.41 * 10^-20 m^2.

2. Calculate the number of collisions per second on one copper atom:
- The collision flux is given as 3.0*10^18 /m2 s1.
- Multiply the collision flux by the surface area of one copper atom to get the number of collisions per second on one copper atom: (3.0*10^18 /m2 s1) * (4.41 * 10^-20 m^2) = 13.23 collisions/s.

3. Calculate the time taken for one copper atom to be covered by a gas atom:
- Since the sticking coefficient is 1.0, it means that all gas atoms that collide with the copper surface will stick to it.
- Therefore, it takes one collision for one copper atom to be covered by a gas atom.
- The time taken for one copper atom to be covered is equal to the inverse of the collision rate on one copper atom: 1 / 13.23 collisions/s = 0.0756 s.

4. Calculate the time taken for a complete monolayer to form:
- A monolayer is formed when all copper atoms on the surface are covered by gas atoms.
- Since the sticking coefficient is 1.0, it means that all gas atoms will stick to the surface.
- Therefore, the time taken for a complete monolayer to form is equal to the time taken for one copper atom to be covered multiplied by the number of copper atoms on the surface.
- The number of copper atoms on the surface is equal to the number of atoms in a square lattice, which is given as (1 / (210 * 10^-12 m))^2 = 1.58 * 10^16 atoms.
- Multiply the time taken for one copper atom to be covered by the number of copper atoms on the surface: 0.0756 s * 1.58 * 10^16 atoms = 1.2 * 10^15 s.

Therefore, the time taken by the gas to form a complete mon