Let's analyze the two sentences to identify whether the underlined words "all" are adjectives or adverbs.

Sentence I: "She lives all alone in her castle."

Here, "all" modifies the adjective "alone". It tells us to what extent she is alone (completely alone). Words that modify adjectives, verbs, or other adverbs are adverbs. Therefore, "all" is an adverb in this sentence.

Sentence II: "All children need love."

Here, "all" modifies the noun "children". It tells us which children (every child). Words that modify nouns or pronouns are adjectives. Therefore, "all" is an adjective in this sentence.

Conclusion:

In Sentence I, "all" is an adverb. In Sentence II, "all" is an adjective.

Related Concepts & Theory

Adjectives

An adjective is a word that describes or modifies a noun or a pronoun. It answers questions like: What kind? Which one? How many?
Example: Five apples, The red car.

Adverbs

An adverb is a word that describes or modifies a verb, an adjective, or another adverb. It often answers questions like: How? When? Where? Why? To what extent?
Example: She ran quickly (modifies the verb 'ran'). She is extremely smart (modifies the adjective 'smart').

The Word "All"

The word "all" can function as different parts of speech depending on its use in a sentence:

• Adjective: When it comes before a noun to describe quantity (e.g., All students passed).
• Adverb: When it modifies an adjective or another adverb to mean 'completely' or 'entirely' (e.g., She is all alone).
• Pronoun: When it stands in for a whole group (e.g., All were present).

You must look at what the word is modifying to determine its part of speech.