Learn Swedish: Du måste ta bort hela skalet från klon. - You must remove the whole shell from the claw.

In Swedish, when you put an adjective in front of a definite noun, you normally have to add a free definite article (like den, det, or de) before the adjective—for example, det tjocka skalet (the thick shell). However, hela (the whole) and halva (half the) are exceptions to this rule. They attach directly to the definite noun without needing the extra article, which is why it is simply hela skalet.

Is it possible to change the word order to ta hela skalet bort?

No, that word order wouldn't work here. Ta bort (remove/take away) is a particle verb, meaning the verb and its attached particle (bort) act together as a single unit of meaning. When the object of a particle verb is a full noun phrase like hela skalet, the particle must come immediately after the verb. You cannot split them up.

What is the indefinite form of klon, and why doesn't it have the usual -en definite ending?

The indefinite form is en klo (a claw). Because it is an "en" word (common gender) that ends in a strongly stressed vowel, it only takes an -n in the definite singular rather than the full -en ending. You see this same pattern with words like en sko (a shoe) becoming skon, or en ko (a cow) becoming kon.