What rule applies most closely to this word?
avail-
group i. if the root is a full word, the ending is usually -able.
group ii. when the root is a full word except for a final e, the forms usually are spelled with -able.
group iii. the suffix -able always follows i.
group iv. when the root has other forms built on the letter a, the -able form is used.
group v. when the root ends in hard c or hard g, -able is used.
group vi. when the root is not a full word,-ible is used.
group vii. when the word has an immediate -tion form, -ible is used.
group viii. when the root ends in ns, miss, or soft c or g, ible is used.