Answer: Element is P, phosphor
Explanation: Phosphor has oxidation number -III and it has 15 protons. So it is possible to have 16 neutrons. Other elements having oxidation number -III are N and As which can not have an isotope with 16 neutrons.
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Carbon dioxide is a compound. Oxygen is an element. A compound is 2 or more elements chemically combined. An element is a pure substance. A mixture is combining two or more different compounds/elements.
Something that melts, something that changes shapes (for instance, play dough being squished), something that boils, something being mixed or dissolved (but only if it doesn't chemically react), etc. A physical change is a change of state of matter.