The six steps of the scientific are:
1. State the question
2. Conduct research
3. Create a hypothesis
4. Perform the experiment
5. Analyze the data
6. Conclusion
So D. would be the correct answer, even though communicating the results could possibly be a step if it's required.
Answer:
a. Sn or Si ⇒ Sn
b. Br or Ga ⇒ Ga
c. Sn or Bi ⇒ similar in size
d. Se or Sn ⇒ Sn
Explanation:
The larger atom has a larger atomic radius. We have to consider how varies the atomic radius for chemical elements in the Periodic Table. In a group (column), the atomic radius increases from top to bottom while in a period (file), it increases from right to left.
a. Sn or Si ⇒ Sn
They are in the <u>same group</u>. Sn is on the top, so it has a larger atomic radius.
b. Br or Ga ⇒ Ga
They are in the <u>same period</u>. Ga is located at the left so it has a larger atomic radius.
c. Sn or Bi ⇒ similar
They are not in the same group neither the same period. Bi is located more at the bottom, so it would be larger than Sn, but Bi is also at the right side, so it would be smaller than Bi. Thus, they have comparable sizes.
d. Se or Sn⇒ Sn
They are not in the same group neither the same period. Se is located at the top and right side compared to Sn, so Sn is the larger atom.
Answer : The combustion is a process in which oxygen is released as a by-product of oxidation-reduction reactions.
Explanation :
Combustion reaction : It is defined as the reactions in which a hydrocarbon reacts with oxygen gas to produce carbon dioxide and water.
The chemical equation of combustion reaction is:

The combustion reaction is also a redox reaction.
Redox reaction or Oxidation-reduction reaction : It is defined as the reaction in which the oxidation and reduction reaction takes place simultaneously.
Oxidation reaction : It is defined as the reaction in which a substance looses its electrons. In this, oxidation state of an element increases. Or we can say that in oxidation, the loss of electrons takes place.
Reduction reaction : It is defined as the reaction in which a substance gains electrons. In this, oxidation state of an element decreases. Or we can say that in reduction, the gain of electrons takes place.
The combustion reaction is also a redox reaction in which the carbon shows oxidation by the addition of oxygen or removal of hydrogen and oxygen shows reduction by the addition of hydrogen or removal of oxygen.
Hence, the combustion is a process in which oxygen is released as a by-product of oxidation-reduction reactions.
It’s the second one if you need more help tell me