<span>Determine the concentration of the ion solvent in solution (moles of solvent/Liter of solution) and then multiply by Avogadro's Number. That will give you the number of ionic atoms of a particular type in that solution.</span>
<u>Answer:</u> The main group metal produce a basic solution in water and the reaction is 
<u>Explanation:</u>
Main group elements are the elements that are present in s-block and p-block.
The metals that are the main group elements are located in Group IA, Group II A and Group III A.
Oxides are formed when a metal or a non-metal reacts with oxygen molecule. There are two types of oxides which are formed: Acidic oxides and basic oxides.
- Acidic oxides are formed by the non-metals.
- Basic oxides are formed by the metals.
When a metal oxide is reacted with water, it leads to the formation of a base.
The general formula of the oxide formed by Group II-A metals is 'MO'
The chemical equation for the reaction of metal oxide of Group II-A and water follows:

Hence, the main group metal produce a basic solution in water and the reaction is 
If you could explain what “merkels” are, the question would be more clear.
Answer:
Error.
Explanation:
An experiment can be defined as an investigation which typically involves the process of manipulating an independent variable (the cause) in order to be able to determine or measure the dependent variable (the effect).
This ultimately implies that, an experiment can be used by scientists to show or demonstrate how a condition causes or gives rise to another i.e cause and effect, influence, behavior, etc in a sample.
Cause and effect can be defined as the relationship between two things or events in which an occurrence one (cause) leads to the occurrence of another (effect).
Experimental error is a factor that can arise from incorrect use of measuring tools or malfunctioning equipment such as thermometer, barometer, multimeter, voltmeter, ammeter, vernier caliper, etc. This error usually causes test results to be inaccurate, incorrect and as such leading to wrong experimental conclusions.
Also, one common example of an experimental error is the error due to parallax.
Answer:
Option (D)
Explanation:
A stream is a narrow river that originates from a source area. These source areas are usually the high altitude mountains in which the high amount of snow is gathered in the winter season and subsequently melts during the summer season. As a result of which the streams and rivers flows and mix up with the seas and oceans. These source areas are commonly termed as the headwaters or the stream head.
The direction towards the headwaters of a stream or moving against the flow direction is generally known as the upstream direction.
Hence, the correct answer is option (D).