This molecule is an ester (a molecule of the form . The parent chain is the unbroken chain containing the carbonyl () group, including the carbonyl carbon. Thus, in the molecule shown, the parent chain consists of four carbons with no double/triple bonds (giving the root ""). The most important functional group is the ester group, so the suffix to the molecule's name is obtained by dropping the "" suffix from the corresponding carboxylic acid and adding "." (thus ). Alkyl groups attached to the ester oxygen are placed before the ester functionality as a separate word.

This molecule is an ester (a molecule of the form . The parent chain is the unbroken chain containing the carbonyl () group, including the carbonyl carbon. Thus, in the molecule shown, the parent chain consists of four carbons with no double/triple bonds (giving the root ""). The most important functional group is the ester group, so the suffix to the molecule's name is obtained by dropping the "" suffix from the corresponding carboxylic acid and adding "." (thus ). The methyl substituent on the parent chain is on carbon number , because the starting carbon in the parent chain is the carbonyl carbon. 

Alkyl groups attached to the ester oxygen are placed before the ester functionality as a separate word.

The longest carbon chain in the molecule has four carbons (thus "") and the lack of double bonds makes it an alkane (thus ""). The highest priority functional group is the carbonyl  group on the end of the chain. The molecule is thus classified as an "aldehyde" because the carbonyl is on the end, and the carbonyl carbon is automatically designated to be carbon number 1 in the chain. When naming aldehydes, they are given the suffix "", so the molecule is called "." Finally, the only other substituent that needs to be mentioned is the bromine on carbon number . Thus, the molecule is .

The molecule shown is an acyl chloride, which is a carboxylic acid derivative. It is named by taking the corresponding carboxylic acid, removing the "" suffix from its IUPAC name, and adding "."

The corresponding carboxylic acid will be the molecule without the chlorine and in its place is a hydroxyl group. This is a carboxylic acid that contains three carbons with no double/triple bonds (Thus ""). Carboxylic acids are named by adding the suffix "" after the parent chain. Thus, the carboxylic acid is called "."

So, taking the name of the corresponding carboxylic acid, removing the "" suffix from its IUPAC name, and adding "" yields "."

When naming an organic compound by the IUPAC, it's best to first start by identifying the functional groups present.

An aldehyde as shown here:

And two ethyl substituents as shown here:

Next, we should identify what functional group has the highest priority, as that will form the base name of the compound:

According to IUPAC convention, Carboxylic Acids and their derivatives have the highest priority then carbonyls (in this case the aldehyde) then alcohols, amines, alkenes, alkynes, and alkanes, so in this case the aldehyde group has the highest priority and therefore makes up the name of the base compound.

Next, we want to number the longest carbon chain with the highest priority functional group with the lowest number. In this case this means we want the carbon on the ring attached to the aldehyde to be carbon number #1, so let's start there and number the carbon chain around the ring.

You should get something like this:

Now that we have numbered the carbon chain we can begin our naming.

Let's start with the base name:

According to IUPAC convention when we have an aldehyde attached to the ring normally (in this case cyclopentane) and put carbaldehyde after it, so in this case the base name is cyclopentanecarbaldehyde.

Next we wish to number ring such that the ethyl substituents have the lowest numbers possible, this is done by making ethyl group next to carbon #1, the second carbon (2-ethyl), then the second ethyl group is 4-ethyl.

Since there are two ethyls the substituents are 2,4-diethyl, so the final name of the compound is 2,4-diethylcyclopentanecarbaldehyde.

Now let's go over the wrong answers:

1) 2,4-diethylcyclopentanal is incorrect because according to IUPAC naming conventions we name the ring normally (cyclopentane) and then put carbaldehyde after its normal name.

2) 2,4-diethylpentanal is incorrect because this compound is a ring and not a straight chain.

3) 3,6-diethylcyclopentanecarbaldehyde is incorrect because the substituents can have lower numbers by making the ethyl group next to the first carbon, 2-ethyl.

4) 3,6-diethylcyclopentanal is wrong because the substituents can have lower numbers by making the ethyl group next to the first carbon, 2-ethyl. Also according to IUPAC naming conventions we name the ring normally (cyclopentane) and then put carbaldehyde after its normal name.