Palmistry—the art of understanding

Using the negation technique.

A Individuals with the same financial status usually DO HAVE a similar personality.
If there is a similarity between financial status & personality, then it will certainly help palmists to make intelligent guesses. It strengthens the argument.

B There is NO stable correlation between an individual's personality and his or her financial status.
If there is no stable correlation, then palmists cannot make intelligent guesses. It weakens the argument.

For the argument to be true, there must be something that could prove that the assertions were intelligent guesses. Option B exactly says that.

Hope it helps.

Palmistry—the art of understanding an individual's present personality and predicting his or her future state through the study of the shape, size, and lines of the hands—is an unscientific technique. In a study, most palmists' assertions about the present financial status of the individuals in the sample population were found to be mere intelligent guesses.

Which one of the following is an assumption necessary to the argument?

A Individuals with the same financial status usually do not have a similar personality. - WRONG. Even if they have it makes no impact on the passage.
B There is a stable correlation between an individual's personality and his or her financial status. - CORRECT. If no correlation existed then intelligent or not the guesses would not have mattered.
C Palmistry is an effective means of predicting how personalities of individuals evolve over the long term. - WRONG. Effective or not it does not matter to conclude as it done in the passage.
D There are numerous other methods for understanding the personality of an individual that are more precise than palmistry. - WRONG. Both red text make this one wrong. Irrelevant to the conclusion.
E The financial future of a person is one of the most important concerns that palmists address. - WRONG. May be true but it does not help in establishing the conclusion as it is. Rather it has no impact on the conclusion.

Answer B.

Understanding the argument - 
Palmistry—the art of understanding an individual's present personality and predicting his or her future state through the study of the shape, size, and lines of the hands—is an unscientific technique. - Conclusion. 
In a study, most palmists' assertions about the present financial status of the individuals in the sample population were found to be mere intelligent guesses. - Supporting premise. 

The argument is like A is B because C. So there needs to be some connection between B and C. 

So, Assumptions here can be 
1. The study is 3rd party - so the study is accurate. 
2. The B is related to C. The financial status is related to the personality. 
3. If Palmistry can't do X, It can't do Y. This means that if Palmistry can't predict the financial status, It can't predict the future state. 
4. Scientific things seldom behave unexpectedly.  

Option Elimination - Assumption

A Individuals with the same financial status usually do not have a similar personality. - The relationship between financial status and personality is not discussed. Moreover, let's negate it. "Individuals with the same financial status usually have a similar personality." So palmists couldn't predict the financial status; Palmistry is an unscientific technique. When negated, it, at best, strengthens the conclusion. So, at best, it's a weakener. 

B There is a stable correlation between an individual's personality and his or her financial status. - Yes. When negated, the conclusion breaks. 

C Palmistry is an effective means of predicting how personalities of individuals evolve over the long term. - What palmistry does is out of scope. 

D There are numerous other methods for understanding the personality of an individual that are more precise than palmistry. - "Other methods" are out of scope. 

E The financial future of a person is one of the most important concerns that palmists address.­ - Whatever the most important concern is is out of scope. Our scope is limited to finding a missing premise for "Palmistry is an unscientific technique."