Answer:
Zero with the subscripts, +2 without them.
Explanation:
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In this case, since we consider that two silicon are bonded with four oxygen atoms to form silicon oxide according to the following chemical equation:

It is also possible to realize it can be simplified to obtain:

Which means that the total charge with the subscripts is zero, and without the subscripts +2 (+4-2).
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Here is a photo to help you out.
It is an example of physical change. The molecules are not changing, so it is not chemical, and a physical property is something that a physical thing has.
combinedAnswer
It can be two or more of the same elements combine together
It can be two or more different elements combined
Step-by-step explanation:
A molecule is a group of two or more atoms that form the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of that substance.
A molecule can also be two or more different elements combined.
Answer:
Oxygen can be made from hydrogen peroxide, which decomposes slowly to form water and oxygen:
hydrogen peroxide → water + oxygen
2H2O2(aq) → 2H2O(l) + O2(g)
The rate of reaction can be increased using a catalyst, manganese(IV) oxide. When manganese(IV) oxide is added to hydrogen peroxide, bubbles of oxygen are given off.
Apparatus arranged to measure the volume of gas in a reaction. Reaction mixture is in a flask and gas travels out through a pipe in the top and down into a trough of water. It then bubbles up through a beehive shelf into an upturned glass jar filled with water. The gas collects at the top of the jar, forcing water out into the trough below.
To make oxygen in the laboratory, hydrogen peroxide is poured into a conical flask containing some manganese(IV) oxide. The gas produced is collected in an upside-down gas jar filled with water. As the oxygen collects in the top of the gas jar, it pushes the water out.
Instead of the gas jar and water bath, a gas syringe could be used to collect the oxygen