1. No, it is impossible.
2. Sometimes it is possible.
3. Yes, it is always possible.

This is correct as far as the ultimate reasons for the commandments are concerned, as it is impossible for our finite human minds to comprehend the infinite wisdom of G-d. It would also be presumptious for us to claim that we can fathom G-d's motivation.

1. No, it is impossible.
2. Sometimes it is possible.
3. Yes, it is always possible.

When the Torah explicitly states a rationale for a particular commandment then we may certainly assume that the reason given is true even though it may not be the sole reason. However the Torah usually does not state the reasons for commandments.

1. No, it is impossible.
2. Sometimes it is possible.
3. Yes, it is always possible.

It is always possible to give rationale for the commandments providing it is understood that the rationale are not the sole reasons for the law, and that the law does not require rationale for its authority.

The rationale given by the famous Jewish commentaries (e.g. Maimonides, Rav S.R. Hirsch), whether they are sociological, psychological, physical or metaphysical are to be understood as benefits and effects of observing the commandments of the Torah.