1) The first reactant is incomplete.
2) The reaction is a combustion reaction and it is easy to infere that it is the combustion of the alkane with 3 carbons.
3) The general chemical formula of the alkanes is

4) Hence the equation is:

5) The name of the alkane is propane, so the word equation is:
propane + oxygen → carbon dioxide + water
6) The equation is unbalanced. This is the balanced equation:

7) It is, as the combustion of any hydrocarbon, a redox (reduction-oxidation) reaction, where the carbon is oxidized and the oxygen is reduced.
8) This kind of reactions release a lot of energy.
Answer:
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Indirect service - photosynthesis
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Answer: C): the number of unpaired electrons.
Explanation: A covalent bond is a type of chemical bond formed by sharing equal number of electrons between two non-metal atoms so that both can attain the a stable octet or duplet structure of noble gases. The electrons shared by two non-metal atoms are the unpaired electrons. For example, in the formation of a chlorine molecule, a chlorine atom has seven valence electrons and electrons usually occur in pairs. Having seven valence electrons means that a chlorine atom has three pairs of electron and one unpaired electron in its outermost shell. The two chlorine atoms will combine together each donating its unpaired electron to be shared, thus leading the two atoms to attain stable octet structure of Argon.
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