Vipin and Javed have salaries in the proportion 4 : 3 respectively. What is Vipin's salary? Statement I: Javed's salary is 75% of Vipin's salary. Statement II: Javed's salary is Rs. 4500.

Introduction / Context:
This data sufficiency question relates to salaries given in a ratio. You are told that the salaries of Vipin and Javed are in the proportion 4 : 3. Two additional statements describe the relationship between their salaries numerically. Your job is to determine whether either statement alone, or both together, are enough to find the actual salary of Vipin in rupees.

Given Data / Assumptions:
- From the question: Vipin's salary : Javed's salary = 4 : 3.
- Question: What is Vipin's salary?
- Statement I: Javed's salary is 75% of Vipin's salary.
- Statement II: Javed's salary is Rs. 4500.
- The ratio 4 : 3 and the 75% relation are consistent with each other.

Concept / Approach:
When given a ratio and a specific amount for one of the terms in the ratio, we can find the other term by simple proportion. The initial ratio 4 : 3 effectively tells us that if Vipin's salary is 4x, then Javed's salary is 3x for some positive value x. Statement I restates the same proportional relationship in percent form, while statement II provides an actual rupee amount for Javed. Data sufficiency asks which combination of these pieces of information is necessary to compute Vipin's salary as a concrete number.

Step-by-Step Solution:
Step 1: Use the ratio from the question. Let Vipin's salary be 4x and Javed's salary be 3x. Step 2: Analyze statement I alone. It says Javed's salary is 75% of Vipin's salary. In algebraic form, this is 3x = 0.75 * 4x. Step 3: Simplify 0.75 * 4x to get 3x, so statement I does not introduce any new numerical amount; it simply confirms the same ratio 4 : 3 that we already have from the question. Step 4: Therefore, statement I alone does not allow us to compute x or Vipin's salary in rupees. It is not sufficient. Step 5: Now analyze statement II alone. It tells us Javed's salary is Rs. 4500. From the ratio, Javed's salary = 3x, so 3x = 4500. Step 6: Solve for x: x = 4500 / 3 = 1500. Step 7: Thus, Vipin's salary is 4x = 4 * 1500 = Rs. 6000. Statement II, together with the ratio given in the question, is enough to determine Vipin's salary. Step 8: Statement I does not add any fresh information beyond the original ratio, so statement II alone is sufficient.

Verification / Alternative check:
We can check that statement I is consistent with the derived salaries. If Vipin earns Rs. 6000 and Javed earns Rs. 4500, then Javed's salary is indeed 75% of Vipin's salary, since 4500 / 6000 = 0.75. The original ratio condition 4 : 3 is also satisfied because 6000 : 4500 reduces to 4 : 3. The calculations are consistent, confirming that statement II gives a unique answer for Vipin's salary when combined with the ratio from the question stem.

Why Other Options Are Wrong:
- Option a is wrong because statement I alone merely restates the same ratio in percentage form and gives no absolute values, so we cannot find Vipin's exact salary.
- Option c is incorrect because only statement II alone is sufficient, while statement I alone is not.
- Option d is wrong because the two statements are not both needed; statement II plus the original ratio is enough.
- Option e is wrong because the data are not insufficient; they clearly allow us to solve for Vipin's salary as Rs. 6000.

Common Pitfalls:
Some students mistakenly think that any statement which seems to give a new equation is automatically sufficient. However, statement I here is just another way of expressing the same ratio, not new numerical data. Another error is to forget that the main question already provides a ratio, and to treat each statement as if it were the only information available. In data sufficiency, the original question text is always part of the information set for evaluating each statement.

Final Answer:
Statement II alone is sufficient to determine Vipin's salary as Rs. 6000, whereas statement I alone is not sufficient. Therefore, the correct data sufficiency choice is option B.