Answer:
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Answer: The given statement is false.
Explanation:
Precipitation reaction is defined as the chemical reaction in which two aqueous solution upon mixing together results in the formation of an insoluble solid.
For example, 
Here AgCl is present in solid state so, it is the precipitate.
But it is not necessarily true that two aqueous solutions will always result in the formation of a precipitate.
For example, 
Hence, we can conclude that the statement precipitation reactions always occur when two aqueous solutions are mixed, is false.
Answer:
1.81 x 10²⁴ atoms
Explanation:
To find the number of atoms in the given number of moles, we need to understand that every substance contains the Avogadro's number of particles.
More appropriately, a mole of any substance will contain the Avogadro's number of particles which is 6.02 x 10²³ atoms
So;
If 1 mole of a substance = 6.02 x 10²³ atoms;
3 mole of MgCl₂ will contain 3 x 6.02 x 10²³ = 1.81 x 10²⁴ atoms