To what decimal place should each answer be rounded? how many significant figures does the rounded answer have?
(a) 101 cm−99.1 cm=1.9 cm (unrounded) after rounding, the answer should be reported to the ( ones place / tenths place / hundredths place ) and thus has (1 significant figure / 2 significant figure / 3 significant figure ) (b) 0.5 atm + 9.8 atm = 10.3 atm (unrounded) after rounding, the number should be reported to the ( ones place / tenths place / hundredths place ) and thus has (1 significant figure / 2 significant figure / 3 significant figure ).

The rounded off figures are as provided in the explanation below.

According to the question;

For Case (a);. 101 cm−99.1 cm=1.9

For Case (b);. 0.5 atm + 9.8 atm = 10.3 atm

The basis for rounding off entails that the place value immediately lower in hierarchy to the place value to be rounded to is considered;

If the digit which occupies this place value is greater or equal to 5; it is rounded to 1 and added to the required place value.

If otherwise, it is rounded to zero, 0 and added to the required digit also.

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These are two questions and two answers

Explanation:

(a) 101 cm−99.1 cm = 1.9 cm (unrounded)

When adding or subtracting quantities, the final result must be rounded to the least number of places in the decimal part of any of the quantities  in the operation.

The number 101 has zero decimals while the number 99.1 has 1 decimal place, so the least number of decimals between those two quantities is 0, so the final result must contain no decimals.

In this case, 1.9 cm, which has two significant figures, must be reported with no decimals, so it must be rounded to one signficant figure, i.e. 2 cm.

After rounding, the answer should be reported to the ( ones place ) and thus has ( 1  significant figure )

(b) 0.5 atm + 9.8 atm = 10.3 atm (unrounded)

Here you are adding two quantities, so use the same rule: round to the least number of places in the decimal part of any of the quantities in the operation.

Both 0.5 atm and 9.8 atm have one decimal (tenths place), so the answer must contain one decimal too, meaning that it stands as 10.3 atm, which has three significant figures.

So, the answer is:

After rounding, the number should be reported to the ( tenths place ) and thus has ( 3 significant figure ).

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.