The key grammar topics covered in English for CBSE Class 9 are:

1. Parts of Speech:
- Noun: Types of nouns, gender, number, case, and usage.
- Pronoun: Types of pronouns, gender, number, case, and usage.
- Verb: Types of verbs, tenses, voice, and usage.
- Adjective: Types of adjectives, degrees of comparison, and usage.
- Adverb: Types of adverbs, degrees of comparison, and usage.
- Preposition: Types of prepositions, and usage.
- Conjunction: Types of conjunctions, and usage.
- Interjection: Types of interjections, and usage.

2. Tenses:
- Present, past, and future tenses.
- Simple, continuous, perfect, and perfect continuous tenses.
- Usage of tenses in different contexts.

3. Subject-Verb Agreement:
- Agreement of verbs with subjects in number and person.

4. Active and Passive Voice:
- Conversion of sentences from active to passive voice and vice versa.
- Identification of active and passive voice in sentences.

5. Direct and Indirect Speech:
- Conversion of sentences from direct to indirect speech and vice versa.
- Reporting verbs, reporting speech, and usage.

6. Transformation of Sentences:
- Conversion of sentences from affirmative to negative, interrogative, and vice versa.
- Conversion of sentences from one type to another (declarative, interrogative, imperative, exclamatory).

7. Modals:
- Usage of modals to express ability, possibility, necessity, permission, etc.

8. Clauses:
- Types of clauses: independent and dependent clauses.
- Identification and usage of clauses in sentences.

9. Sentence Structure:
- Subject, predicate, object, complement, and modifiers.
- Types of sentences: simple, compound, complex, and compound-complex sentences.

10. Punctuation:
- Usage of punctuation marks: full stop, comma, colon, semicolon, apostrophe, quotation marks, etc.

11. Articles:
- Usage of articles: a, an, the, and zero article.

12. Agreement of Pronouns:
- Agreement of pronouns with antecedents in number, gender, and person.

13. Sentence Correction:
- Identifying and correcting grammatical errors in sentences.

14. Vocabulary:
- Building vocabulary through word formation, synonyms, antonyms, etc.

These key grammar topics are essential for developing a strong foundation in English grammar and language skills. They enable students to understand and construct grammatically correct sentences, enhance their communication skills, and improve their overall proficiency in the English language.