Which would show an example of how physical changes are reversible? cutting a gold bar in two pieces and then putting the pieces next to each other burning a match and then relighting it melting tin and then cooling it into a mold combining sodium and chlorine to make the new material of table salt

Answer : The correct option is, melting tin and then cooling it into a mold.

Explanation :

Chemical change : It is a change where changes occurs in the chemical composition and thus resulting in the formation of new compound or substance. It is an irreversible reaction.

Physical change : It is a change in which shape and size of a substance changes. In this there is no change in the chemical composition of the substance and no new substance is forming. It is a reversible reaction.

(1) Cutting a gold bar in two pieces and then putting the pieces next to each other : It is a physical change because only changes takes place in the shape or size of the substance but it can not be reversible.

(2) Burning a match and then relighting it : It is a chemical change because in this process, chemical reaction takes place by burning that means changes occurs in the chemical composition and new compound is formed.

(3) Melting tin and then cooling it into a mold : It is a physical change and a reversible process because in this process, only phase changes and it can also be reversible by again melting process.

(4) Combining sodium and chlorine to make the new material of table salt : It is a chemical change because in this process, chemical reaction takes place that means changes occurs in the chemical composition and new compound is formed.

Hence, the correct option is, melting tin and then cooling it into a mold.

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

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