Answer;
No, sometimes it just causes a physical change, such as ice melting to water.
Explanation;
-The difference between a physical reaction and a chemical reaction is composition. In a chemical reaction, there is a change in the composition of the substances in question; in a physical change there is a difference in the appearance, smell, or simple display of a sample of matter without a change in composition.
Heating a substance may cause a physical change or a chemical change. For example melting ice to water, involves supplying heat to change ice into water which is a chemical change.
-On the other hand, an example of decomposition reactions are chemical reactions which involves supplying heat to a substance; for example decomposing copper (II) nitrate which yields, copper (ii) oxide, nitrogen (iv) oxide and oxygen gas, is chemical reaction.
<u>Answer:</u> In 
molecule, there are 2 atoms of hydrogen present.
<u>Explanation:</u>
Coefficients are defined as the numbers that are written in the front of atoms or molecules during a chemical reaction. They represent the number of moles of the substance present in a chemical reaction.
<u>For Example:</u> 
2 moles of hydrogen gas is reacting with 1 mole of oxygen gas to produce 2 moles of water molecule.
Subscript numbers are defined as the number of atoms of each element present in a compound.
<u>For Example:</u> In 
, 2 atoms of oxygen element is there and 1 atom of carbon element is there.
Superscript numbers are defined as the charges of ions reacting in a chemical reaction.
<u>For Example:</u> In 
, 2+ charge is present on calcium ion.
We are given:
A molecule of hydrogen which is
The number '2' is present in subscript, which represents the number of atoms in a molecule or a compound.
Hence, in molecule, there are 2 atoms of hydrogen present.
