Answer:

In the given sentence, we need to choose a suffix that can form a word to complete the sentence. The sentence is "Happi_______ is a state of mind. It does not depend on others."

The word "Happi" is the root word, and we need to choose a suffix that can complete the word and make it fit in the sentence. Let's analyze the given options:

a) -ness: The suffix "-ness" is used to form abstract nouns from adjectives. For example, "happiness" is the abstract noun form of the adjective "happy". In this case, adding "-ness" to the root word "Happi" will give us "Happiness", which fits in the sentence and makes it grammatically correct. The sentence will become "Happiness is a state of mind. It does not depend on others." This option is correct.

b) -able: The suffix "-able" is used to form adjectives that express the idea of possibility or capability. For example, "comfortable" means able to be comforted. Adding "-able" to the root word "Happi" will give us "Happiable", which is not a commonly used word and does not fit in the sentence. This option is incorrect.

c) -ible: The suffix "-ible" is used to form adjectives that express the idea of possibility or capability. It is similar to "-able". Adding "-ible" to the root word "Happi" will give us "Happible", which is not a commonly used word and does not fit in the sentence. This option is incorrect.

d) -ent: The suffix "-ent" is used to form adjectives from nouns or verbs. For example, "dependent" means relying on someone or something. Adding "-ent" to the root word "Happi" will give us "Happient", which is not a commonly used word and does not fit in the sentence. This option is incorrect.

Therefore, the correct answer is option 'A' -ness.