There are 3 sig figs. 8 and 2 are obvious. The ending 0 is significant because it is at the end of a decimal number, and doesn't have to be measured.
Answer: hen a solution is very acidic, what does it have a high concentration of?
Hydroxide (OH-)
Hydronium (H3O+)
Iodide (I-)
Acetate(C2H3O2-)
Explanation:
Answer: matter and its interaction with energy. Matter has mass and occupies space. A Substance is matter that cannot be separated into other kinds of matter by physical means.
Explanation:

The relationship between mass of matter per unit volume is known as :

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x=3
Use the pythagorean theorem:
a^2 + b^2 = c^2
4^2 + x^2 = 5^2
16 + x^2 = 25
x^2 = 25-16
x^2 = 9
√x^2 = √9
x = 3