Why are chemical reactions often carried out using solutions? the heterogenous nature of solutions prevents the reactants from freely mixing. the amount of each reactant can be controlled by adjusting the volume of each solution that is used. even very small amounts of reactants can be combined by using dilute solutions. a color change will always occur when a reaction is conducted in solution. the molecules or ions in a solution can freely intermingle. the solvent must always be water, so it is impossible for a fire to start.

The molecules or ions in a solution can freely intermingle.  

Explanation:

The reactant molecules and ions can move freely in solution, so thy are more likely to collide with each other and form products.

A is wrong. Solutions are homogeneous.

B and C are wrong. The statements are correct, but they are not the reason why reactions are carried out in solution.

D is wrong. Chemical reactions do not always produce a colour change.

F is wrong. Some chemicals react with water, so other (often flammable) solvents must be used.

answer: - 3.) the oxidation state of nitrogen in no changes from +2 to 0, and the oxidation state of carbon in co changes from +2 to +4 as the reaction proceeds.

solution: - as per the rules, oxidation number of oxygen in its compounds is -2. the sum of oxidation numbers of all the elements of a molecule or compound is zero.

also, the oxidation number in elemental form is zero.

in no, the oxidation number of o is -2 so the oxidation number of n is +2 so that the sum is zero.

similarly, the oxidation number of c in co is +2 and o is -2.

on product side the oxidation number of n is 0 as it is in the elemental form() .

oxidation number of c in carbon dioxide is +4 as there are two oxygen in it and we know that each oxygen is -2.

so, oxidation number of n is changing from +2 to 0 and the oxidation number of c is changing from +2 to +4.

since nitrogen is reduced and hence no is acting as an oxidizing agent. carbon is oxidized and so co is acting as a reducing agent.

so, the right choice is number 3.)the oxidation state of nitrogen in no changes from +2 to 0, and the oxidation state of carbon in co changes from +2 to +4 as the reaction proceeds.

the answer would be b i believe