Explanation:
Atomic number is defined as the number of an element which represents total number of protons.
When an atom is neutral then it means it contains same number of protons and electrons.
On the other hand, atomic mass is defined as the sum of total number of protons and neutrons present in an atom.
Protons of every element remains fixed because it shows the identity of each element but if we change the number of neutrons then also identity of the atom will remain fixed. This is because changing the number of neutrons will not show any change in number of protons.
For example, 
and 
are isotopes of hydrogen and they have same number of protons but different number of neutrons.
Thus, we can conclude that number of neutrons can vary without changing the identity of the element.
Answer:
Oxygen and Chlorine
Explanation:
Covalent bonds involve the sharing of electrons between nonmetals.
<u>Answer:</u>
<em>The system is the Answer
</em>
<em></em>
<u>Explanation:</u>
System is the region which is taken into consideration.
While we perform a chemical reaction the system is the substance taken in the container.
So, A thermodynamic system is the amount of matter or the region in universe which is under the study.
The region outside the beaker are called as surroundings.
The beaker (the surface which separates the system from its surroundings) is said to be the boundary
System + surroundings = universe
Natural selection and selective breeding can cause both animal and plant changes. The distinction between the two is that natural selection occurs without human intervention, while selective breeding occurs only when humans interfere. As a result, selective breeding is also known as artificial selection.
<span>i think the answer should be 2KOH +H2SO4=K2SO4+2H20</span>
