**Given:**
- Charges at corners A and B: 2 x 10^-6 C and 1 x 10^-6 C
- Side of the square: 5 cm

**To find:**
- Work done against the electric field in moving a charge of 1 x 10^-6 C from C to D

**Explanation:**
To find the work done against the electric field, we need to calculate the change in potential energy of the charge as it moves from C to D. The work done can be calculated using the formula:

Work = Change in potential energy = q * ΔV

Where q is the charge and ΔV is the change in potential.

**Step 1: Calculating the potential at points C and D**
The potential at a point due to a charge can be calculated using the formula:

V = k * q / r

Where V is the potential, k is the electrostatic constant (9 x 10^9 Nm^2/C^2), q is the charge, and r is the distance from the charge.

For point C:
- The distance from charge A is the diagonal of the square, which can be calculated using the Pythagorean theorem: r = √(5^2 + 5^2) = √50 cm
- The charge at A is 2 x 10^-6 C
- Plugging the values into the formula, Vc = (9 x 10^9 Nm^2/C^2) * (2 x 10^-6 C) / (√50 cm) = 9 x 10^9 V

For point D:
- The distance from charge B is the side of the square, which is 5 cm
- The charge at B is 1 x 10^-6 C
- Plugging the values into the formula, Vd = (9 x 10^9 Nm^2/C^2) * (1 x 10^-6 C) / (5 cm) = 1.8 x 10^9 V

**Step 2: Calculating the change in potential**
The change in potential (ΔV) is given by the difference between the potentials at points C and D:

ΔV = Vd - Vc = (1.8 x 10^9 V) - (9 x 10^9 V) = -7.2 x 10^9 V

**Step 3: Calculating the work done**
The work done can be calculated by multiplying the charge (1 x 10^-6 C) by the change in potential (-7.2 x 10^9 V):

Work = q * ΔV = (1 x 10^-6 C) * (-7.2 x 10^9 V) = -7.2 x 10^-3 J

Therefore, the work done against the electric field in moving a charge of 1 x 10^-6 C from C to D is -7.2 x 10^-3 J. The negative sign indicates that work is done against the electric field.