Introduction:
The magnitude of acceleration of blocks is determined by the net force acting on them according to Newton's second law of motion. In this scenario, we have two blocks of mass 2 kg and 4 kg, and we need to calculate their respective accelerations.

Newton's Second Law of Motion:
Newton's second law of motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, it can be expressed as:

F = ma

where F is the net force acting on the object, m is the mass of the object, and a is the acceleration of the object.

Calculating the Acceleration:
To calculate the magnitude of acceleration of the blocks, we need to consider the forces acting on each block.

Block with Mass 2 kg:
Let's consider the block with a mass of 2 kg. The only force acting on this block is the force of gravity, which can be calculated using the formula:

F = mg

where m is the mass of the block and g is the acceleration due to gravity (approximately 9.8 m/s^2).

F = 2 kg * 9.8 m/s^2
F = 19.6 N

Since there are no other forces acting on the block, the net force (F_net) is equal to the force of gravity (F).

F_net = F = 19.6 N

Using Newton's second law of motion, we can find the acceleration (a1) of the block:

F_net = ma1
19.6 N = 2 kg * a1
a1 = 19.6 N / 2 kg
a1 = 9.8 m/s^2

Thus, the magnitude of acceleration for the block with a mass of 2 kg (a1) is 9.8 m/s^2.

Block with Mass 4 kg:
Now, let's consider the block with a mass of 4 kg. Similar to the previous block, the only force acting on this block is the force of gravity.

F = mg
F = 4 kg * 9.8 m/s^2
F = 39.2 N

Since there are no other forces acting on the block, the net force (F_net) is equal to the force of gravity (F).

F_net = F = 39.2 N

Using Newton's second law of motion, we can find the acceleration (a2) of the block:

F_net = ma2
39.2 N = 4 kg * a2
a2 = 39.2 N / 4 kg
a2 = 9.8 m/s^2

Thus, the magnitude of acceleration for the block with a mass of 4 kg (a2) is also 9.8 m/s^2.

Conclusion:
In conclusion, the magnitude of acceleration for both the block with a mass of 2 kg and the block with a mass of 4 kg is 9.8 m/s^2. This is because the force of gravity is the only force acting on the blocks, and according to Newton's second law of motion, the acceleration is directly proportional to the net force and inversely proportional to the mass.