Dan wants to test the effects of different amounts of antibiotic on bacteria. While setting up his experiment he makes sure to use the same type of antibiotic, the same type of bacteria, and the same type of incubator for each trial. Which phrase below best describes this part of the experiment?

C

Explanation:

A. analyzing results

B. collecting data

C. choosing controlled variables

D. making a prediction

The correct answer would be choosing controlled variables.

The controlled variables are factors that are kept constant among the different groups of subjects during the course of an experiment so as to be able to isolate the effects of a single factor - the independent variable.

There are basically 3 types of variables in a scientific experiment;

1. The independent variable

2. The dependent variable

3. The controlled variable

The independent variables are the variables whose effects are to be determined in the course of experiments. The dependent variables are the variables that are actually measured during the course of experiments and whose values vary along with that of the independent variables. The controlled variables are other variables required for the experiment but which must be kept constant among subjects in order to be able to isolate the effects of the independent variable.

The correct option is C.

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.