Answer:
The gravitational force between m₁ and m₂, is approximately 1.06789 × 10⁻⁶ N
Explanation:
The details of the given masses having gravitational attractive force between them are;
m₁ = 20 kg, r₁ = 10 cm = 0.1 m, m₂ = 50 kg, and r₂ = 15 cm = 0.15 m
The gravitational force between m₁ and m₂ is given by Newton's Law of gravitation as follows;

Where;
F = The gravitational force between m₁ and m₂
G = The universal gravitational constant = 6.67430 × 10⁻¹¹ N·m²/kg²
r₂ = 0.1 m + 0.15 m = 0.25 m
Therefore, we have;

The gravitational force between m₁ and m₂, F ≈ 1.06789 × 10⁻⁶ N
The reaction 4Al + 3O₂ → 2Al₂O₃ is a synthesis or also called combination reaction because reactants combine to produce a new compound (Option 2).
<h3>What is a synthesis combination reaction?</h3>
In chemistry, a synthesis or combination reaction is any type of chemical reaction in which two or more molecules called reactants combine to produce one or more molecules called products of such reaction.
Therefore, with this data, we can see that a synthesis or combination reaction is a chemical process where two or more molecules combine to produce a new molecule known as a product.
Learn more about synthesis combination reactions here:
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"The rock has a downward acceleration of 9.8 m/s2" is the one among the following choices that explains the <span>rock’s acceleration at the instant that it reaches the top of its trajectory (where its velocity is momentarily zero). The correct option among all the options that are given in the question is option "D". </span>