Which statement correctly describes Newton's Second Law of Motion and its applications in the provided scenarios?

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. This is represented by the formula $F = ma$, or $a = \frac{F}{m}$.

A) Inversely proportional to force and directly proportional to mass - Incorrect.
B) Directly proportional to net force and inversely proportional to mass - Correct.
C) Equal to mass multiplied by velocity - This describes momentum, not acceleration. Incorrect.
D) Constant for all objects - Incorrect, acceleration depends on force and mass.

The correct option is B.

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction.

A) A greater reaction - Incorrect.
B) An equal and opposite reaction - Correct.
C) A smaller reaction - Incorrect.
D) No reaction in a vacuum - Incorrect.

The correct option is B.

Given:
Mass ($m$) = $10\, \text{kg}$
Net force ($F$) = $50\, \text{N}$
We need to find the acceleration ($a$).

Newton's Second Law is given by the formula:

To find acceleration, rearrange the formula:

A) $5\, \text{m/s}^2$ - Correct.
B) $500\, \text{m/s}^2$ - Incorrect.
C) $0.5\, \text{m/s}^2$ - Incorrect.
D) $50\, \text{m/s}^2$ - Incorrect.

The correct option is A.

The property of matter that resists changes in motion (i.e., resists acceleration) is called inertia.

A) Friction: Friction is a force that opposes motion between surfaces in contact. While it resists motion, it is a force, not the fundamental property of matter (inertia) that resists changes in motion.
B) Weight: Weight is the force of gravity acting on an object's mass. It is not related to resisting changes in motion.
Since "Inertia" is not a visible option, and we must select from the given options, "Friction" is the only option that describes a form of resistance to motion, even though it is a force and not the fundamental property of matter (inertia) that resists changes in motion.

The correct option among the visible choices, based on the concept of resistance to motion, is A.