Write the IUPAC name of `CH_3 underset(Cl) underset(| ) CH CH_2 CHO.`

Explanation

To write the IUPAC name of the compound `CH₃ClCH=CH₂CHO`, we will follow these steps:

### Step 1: Identify the Functional Group
The compound contains an aldehyde functional group (−CHO). In IUPAC nomenclature, the aldehyde group takes priority and must be given the lowest possible number.

### Step 2: Determine the Longest Carbon Chain
Count the number of carbon atoms in the longest continuous chain that includes the aldehyde group. Here, we can see that the longest chain has 4 carbon atoms.

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