What rule applies to this word? desire 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

The correct answer is Group II. "When the root is a full word except for a final "e", the forms usually are spelled with -able".

Explanation:

In language, a root word refers to the basic unit of a word that cannot be reduced to a smaller unit. Because of this, new words can be formed by adding prefixes or suffixes which are letters or syllables placed before or after root words. However, in most cases, the use of suffixes and prefixes follow strict grammatical rules that work as a guide to add a prefix or suffix depending on the root word. This is the case of the suffix "-able" that means capable of and which is added to root words according to different rules described in the question which classifies root words according to eight different groups and describes in which way should the suffix "-able" added according to the features of the root word.

For the word "desire" which means  the action of wishing something, the rule that applies to this word is the one described in Group III or "When the root is a full word except for a final "e", the forms usually are spelled with -able" considering the word desire is a full word that cannot be reduced to shorter units and it also ends in "-e", therefore the suffix is added by omitting the "-e" which means the word becomes "desirable" and means  something attractive or capable of being desired. Thus, the rule that applies to the word "desire" is Group II.

what is the question?