Explain the following statement: “An asset held as part of a portfolio is generally less risky than the same asset held

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Explain the following statement: “An asset held as part of a
portfolio is generally less risky than the same asset held in
isolation.”
What is meant by perfect “positive correlation,” “perfect
negative correlation,” and “zero correlation”?
In general, can the risk of a portfolio be reduced to zero by
increasing the number of stocks in the portfolio? Explain.
Stock A’s returns in the past 5 years have been 10%, −15%, 35%,
10%, and −20%. Stock B’s returns have been −5%, 1%, −4%, 40%, and
30%. What is the correlation coefficient for returns between Stock
A and Stock B? (−0.35)