Check all the statements that are correct. conservation of mass means:

a. we can start a reaction with different types of elements than we have at the end of the reaction.

b. matter cannot be created

c. we must start and end with the same amounts of matter

d. matter can be destroyed in a chemical reaction

B. Matter cannot be created

C. We must start and end with the same amounts of matter  

Explanation:

Matter is anything that has mass. Thus, if mass is conserved, matter must also be conserved.

A. is wrong. We cannot convert one type of matter into another.

D. is wrong. Matter cannot be destroyed in a chemical reaction.

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.