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Problem: Determine the IUPAC names of the given organic molecules.

#### Step-by-Step Solution:

---

Question 1:

Molecule:
```
Br
CH3CHCHCH3
CH2CH3
```

#### Analysis:
1. Identify the parent chain: The longest continuous carbon chain has 5 carbons, so the parent chain is pentane.
2. Locate substituents:
- There is a bromine atom (Br) on the second carbon.
- There is an ethyl group (CH₂CH₃) on the third carbon.
3. Number the chain: Start numbering from the end that gives the lowest possible numbers to the substituents. Here, numbering from the left gives:
- Bromine on C-2.
- Ethyl group on C-3.
4. Name the compound: The IUPAC name is 2-bromo-3-ethylpentane.

#### Correct Answer:
(C) 2-bromo-3-methyl/pentane

---

Question 2:

Molecule:
```
CH3
CH2CHCH=CHCH3
CH3
```

#### Analysis:
1. Identify the parent chain: The longest continuous carbon chain has 6 carbons, so the parent chain is hexene.
2. Locate the double bond: The double bond is between C-2 and C-3.
3. Locate substituents:
- There are methyl groups (CH₃) on C-2, C-3, and C-5.
4. Number the chain: The double bond determines the numbering, starting from the end closest to it. The methyl groups are on C-2, C-3, and C-5.
5. Name the compound: The IUPAC name is 2,3,5-trimethylhex-2-ene.

#### Correct Answer:
(A) 2,3,5-trimethylhex-2-ene

---

Question 3:

Molecule:
```
CH3
CH2CHCH2CH2CH3
CH3
CH3
```

#### Analysis:
1. Identify the parent chain: The longest continuous carbon chain has 6 carbons, so the parent chain is hexane.
2. Locate substituents:
- There are two methyl groups (CH₃) on C-2 and C-4.
3. Number the chain: Start numbering from the end that gives the lowest possible numbers to the substituents. Here, numbering from the left gives:
- Methyl groups on C-2 and C-4.
4. Name the compound: The IUPAC name is 2,4-dimethylhexane.

#### Correct Answer:
(A) 2,4-dimethylhexane

---

Question 4:

Molecule:
```
CH3
CH2CH=C(CH3)CH2CH3
CH3
```

#### Analysis:
1. Identify the parent chain: The longest continuous carbon chain has 5 carbons, so the parent chain is pentene.
2. Locate the double bond: The double bond is between C-2 and C-3.
3. Locate substituents:
- There is an ethyl group (CH₂CH₃) on C-4.
- There is a methyl group (CH₃) on C-2.
4. Number the chain: The double bond determines the numbering, starting from the end closest to it. The ethyl group is on C-4, and the methyl group is on C-2.
5. Name the compound: The IUPAC name is 4-ethyl-2-pentene.

#### Correct Answer:
(A) 4-ethyl/pent-2-ene

---

Final Answers:

1. (C) 2-bromo-3-methyl/pentane
2. (A) 2,3,5-trimethylhex-2-ene
3. (A) 2,4-dimethylhexane
4. (A) 4-ethyl/pent-2-ene

Boxed Final Answer:
\[
\boxed{C, A, A, A}
\]