How many of the following are oxidation-reduction reactions?
I. reaction of a metal with a nonmetal
II. synthesis
III. combustion
IV. precipitation
V. decomposition

a.5

b.3

c.2

d.1

e.4

e.4

Explanation:

An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation-reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron.

I. reaction of a metal with a nonmetal

In these reactions, electrons is usually being lost by metals and gained by non metals. This is a redox reaction.

II. synthesis

Using the following example;

3 H2(g) + N2(g) → 2 NH3(g)

The oxidation number of the elements usually change from their ground state (0) to a higher or lesser value. This is a redox reaction.

III. combustion

A combustion reaction is a redox reaction between a compound and molecular oxygen to form oxygen-containing products.

IV. precipitation

Precipitation reactions almost always are not redox reactions because here is no change in the oxidation numbers of the atoms.

V. decomposition

Decomposition reactions are the reverse of combination reactions / synthesis, meaning they are the breakdown of a chemical compound into its component elements. Decomposition reactions are usually redox reactions.

there is none because earth is stationary and flat.

the dissolution of polymer can be thermodynamically described in 2 steps.