Answer: (a) There are 0.428 moles present in 12 g of
molecule.
(b) There are 2 moles present in
particles of oxygen.
Explanation:
(a). The mass of nitrogen molecule is given as 12 g.
As the molar mass of
is 28 g/mol so its number of moles are calculated as follows.

So, there are 0.428 moles present in 12 g of
molecule.
(b). According to the mole concept, 1 mole of every substance contains
atoms.
Therefore, moles present in
particles are calculated as follows.

So, there are 2 moles present in
particles of oxygen.
These 5 metals are: zinc,copper,tin,bronze,nickel
1,516.31168 grams of Magnesium Hydroxide
Answer A) : We have to calculate the number of moles of Benzene involved in the reaction,
30 g / 78 moles of benzene = 0.384 moles
For bromine it will be the same process,
65 g / 159.8 moles = 0.406 moles
By observing the reaction given above we can say that the reaction ratio of bromine and benzene is 1 : 1
We need to find the mass of bromobenzene,
which should be, 6(12) + 5 (1)+ 79.90 = 156.9 g/mol
So, the mass of bromobenzene will be 156.9 g/mol X 0.3846 mol = 60.343 g
Hence the theoretical yield will be 60.34 g
Answer B) : To calculate the actual yield we have to divide it with theoretical yield.
(56.7g / 60.343 g ) X100% = 93.96 %
Here, we can say that we got 93.96 % of actual yield.
As we know it is impossible to get 100% yield in any reaction.
When sodium carbonate is dissolved in water, the equation is
.
When carbon dioxide is placed in water, aqueous carbon dioxide is formed: 
<h3>Dissolution of compounds in water</h3>
Some compounds are water-soluble, some are just partially soluble, while others are insoluble in water. Some soluble or partially soluble substances dissociate in water into their component ions. These substances are said to be ionic.
Sodium carbonate, like every other sodium salt, is soluble in water. It dissolves in water to form an aqueous solution of sodium carbonate.
While in solution, sodium carbonate dissociates into its component ions according to the following equation:

Carbon dioxide, on the other hand, does not dissociate in water. Instead, it dissolves in water where most of it remains as aqueous carbon dioxide in equilibrium with a small amount of hydronium ion and hydrogen carbonate ion.
Since the hydronium and hydrogen carbonate ions formed are so minute, the equation of the reaction can be written as: 
More on the dissolution of substances can be found here: brainly.com/question/28580758
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