I think the correct answer is C
Force = mass x acceleration
Force = 4kg x 10m/s^2
Force = 40N
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2. Learners give priority to evidence, allowing them to develop and
evaluate explanations that address scientifically-oriented questions.
3. earners formulate explanations form evidence to address scientifically
oriented question
4. Learners evaluate their explanations in light of alternative explanations,
particularly those reflecting scientific understanding.
5. Learners communicate and justify their proposed explanations.
the number of neutrons may b 21
Answer:

Explanation:
The original equation is:

We notice that:
- we have 1 atom of Fe on the left, and 2 atoms of Fe on the right
- we have 2 atoms of O on the left, and 3 atoms of O on the right
Therefore, the equation is not balanced.
In order to balance it, we can add:
- a coefficient 3 in front of 
- a coefficient 2 in front of 
So we have:

Now the oxygen is balanced, but the iron it not balanced yet, since we have 1 Fe on the left and 4 on the right. Therefore, we should add a coefficient 4 on the Fe on the left:
