It’s basically that’s any system that’s closed to all transfers of matter and energy the mass of the system has to remain constant over time because they can’t change meaning you can’t add or remove from it
<span>A physical change basically involves a change in physical properties. Some examples of physical properties include: texture, shape, size, color, volume, mass, weight, etc.
The water melting has changed the shape and therefore it's physical properties, but the chemical nature of the water has not been altered.
So that's why it's a physical change, and not a chemical change.</span>
A. Filtration
This is because of the layers of Filter it goes through to make sure it is pure.

As depth increases, the density of the layers decreases.
Answer:
d
Explanation:
Carbohydrates are compounds containing carbon, hydrogen, and oxygen. Therefore, a is true.
An empirical formula is the simplest ratio of atoms present in a compound. Therefore, C2H4O2 and C3H6O3, (if you simplified them like you would a fraction) would be CH2O. Therefore b is correct,
They also have the same % composition, with a ratio of 1 carbon : 2 hydrogen : 1 oxygen. Therefore, c is correct.
Since a, b and c are all correct, the answer is d, all of the above are true.