Explanation:
A change that does not cause any change in chemical composition of a substance is known as a physical change.
For example, mass, density, volume etc are all physical changes.
On the other hand, a change that brings change in chemical composition of a substance is known as chemical change.
For example, combustion, toxicity, reactivity etc are all chemical changes.
Hence, following statements are identified as chemical or physical changes as follows.
(a) Oxygen gas supports combustion : Chemical change
(b) Fertilizers help to increase agricultural production : Chemical change
(c) Water boils below 
on top of a mountain : Physical change
(d) Lead is denser than aluminum : Physical change
(e) Uranium is a radioactive element : Chemical change
The group is called the noble gas i think
Explanation:
The periodic table arranges elements based on their atomic numbers in a systematic fashion.
There are about 110 elements on the periodic table with each of them having their unique atomic numbers.
On periodic table, most atoms are designated as:
ₓⁿT
T is the symbol of the atom
X is the atomic number of the atom
n is the mass number
Atomic number is the number of protons in atoms in an element. Protons are the positively charged particles.
Mass number is the number of protons and neutrons in an atom. Both protons and neutrons are in the nucleus of an atom.
Atomic number = number of protons = number of electrons
Mass number = number of protons + number of neutrons
Number of neutrons = mass number - number of protons
Number of neutrons = mass number - atomic number
learn more:
Periodic table brainly.com/question/2014634
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