Two statements are given, followed by two conclusions numbered I and II. Assuming the statements to be true, even if they seem to be at variance with commonly known facts, decide which of the conclusions logically follow(s) from the statements.

Statements:

All pebbles are stones.

No stones are shells.

Conclusions:

I. Some pebbles are shells.

II. No shells are stones.

The correct option is Only conclusion II follows.

Let us analyze the given statements step-by-step:
1. All pebbles are stones: This means the category of "pebbles" is completely contained within the category of "stones".
2. No stones are shells: This means there is no intersection or overlap between the category of "stones" and the category of "shells". They are disjoint sets.

Now, let us evaluate each conclusion based on these statements:
Conclusion I: Some pebbles are shells.
Since all pebbles are stones, and no stones are shells, no pebbles can ever be shells. Therefore, Conclusion I does not follow.
Conclusion II: No shells are stones.
Since statement 2 clearly establishes that "No stones are shells", it is logically equivalent to say that "No shells are stones" because the relationship of exclusion is mutual. Therefore, Conclusion II logically follows.

Hence, only conclusion II follows.