Am in a at least 150 words, justify the need for a control in an experiment. use complete sentences.

You need a control group in an experiment because if you did not have a control group your numbers or outcomes can cause an error because you wont have any numbers that are right to compare to. There will be too many things changed in the trial.

The need for control in a experiment is to make a base line for you to compare other data that you have collected. like in some tests it would be the group that you would start with then you will have another group that had the same amount of whatever and it will help you.

For example, you want to find out if a certain class makes student get bored faster. so you have three groups: A-math (control), B-reading, C-science. you ask multiple different students.

at the end of the day you see how many people voted for everything, and you compare it with the control. if groups B and C had the same amount of votes as A then it wont work.

if B and C had the same amount but less than A it would work.

if B and C had the same but less than A it would mean that not all the classes are boring, but one class makes quite a difference in the results.

is what i said put it in your own words though.

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.