A solution is when a solute is added to a water solvent. Since water is neutral, the charge of the said solution is dictated by the charge of the ion. This is the subscript of the element. If it is not stated, then we use the common ion form.
1. H: The charge for hydrogen ion is +1.
2. OH⁻: The charge is ⁻1.
3. Mg2: This ion has a charge of +2.
4. HSO₄⁻: -1
5. SO₄²⁻: -2
6. Mg(HSO₄): This is not an ion, but an undissociated compound. So, it has a neutral charge of 7.
7. Mg(OH): Neutral at pH 7
8. Na: Sodium ion has a charge of +1.
9. NO₃⁻: -1.
The dependent variable is the variable that changes based on the independent variable (the manipulated variable).
Answer:
a.Archaeopteryx
b.Archaeopteryx had more in common with other small Mesozoic dinosaurs than with modern birds.Archaeopteryx was generally accepted by palaeontologists and popular reference books as the oldest known bird.Archaeopteryx could grow to about 0.5 m (1 ft 8 in) in length.
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The pressure gets increased to 486 kPa from 405 kPa, when the volume is decreased from 6 cm³ to 4 cm³.
Explanation:
In the present problem, the temperature is said to remain at constant and there is change in the pressure. So according to Boyle's law, the relationship between pressure and volume of any gaseous objects are inversely related to each other. In other words, the pressure attained by gas molecules in a container will be inversely proportional to the volume of the gas molecules occupied in the container, at constant temperature.

So, if two volumes V₁ and V₂ are considered, then their respective pressure will be represented as P₁ and P₂. Then, as per Boyle's law,

So let us consider, V₁ = 6 cm³ and V₂ = 4 cm³ and pressure P₁ = 405 kPa and we have to determine P₂.
Then, 
So, the pressure at new volume of 4 cm³ is 486 kPa. It can be seen that as there is decrease in the volume, there is an increase in the pressure. So it satisfied the Boyle's law.
Thus, the pressure gets increased to 486 kPa from 405 kPa, when the volume is decreased from 6 cm³ to 4 cm³.