What's the answer? please help​

a usually reversible change in the physical properties of a substance, as size or shape

For example:

Freezing a liquid is a physical change.

Many financial investors use a simple rule of thumb to determine how an individual should allocate their personal investments:

1 - your age = % of investments held in stocks

In this case, Jeff should hold 78% of his investments in stocks:

stocks provide the best returns in the long run, and Jeff has a lot of time until retirementdue to his young age, Jeff can afford the risk of investing heavily in stocks

The remaining 22% should be invested in bonds which carry a much lower risk but yield lower gains.