"Im" usually means "not" or "opposite of":
* Immature: Not mature
* Impossible: Not possible
* Impatient: Not patient
* Impartial: Not partial or biased
* Imperfect: Not perfect
* Impolite: Not polite
* Immoral: Not moral
* Immune: Not susceptible to disease
* Immigrant: A person who comes to live permanently in a foreign country
* Impact: To have a strong effect
* Impatient: Not patient
* Impress: To make a strong impression on someone
* Improbable: Not likely to happen
* Improve: To make better
* Improvise: To create something without preparation
"In" usually means "not" or "the opposite of":
* Inactive: Not active
* Inaccurate: Not accurate
* Incapable: Not capable
* Incompetent: Not competent
* Incomplete: Not complete
* Incorrect: Not correct
* Inconsiderate: Not considerate
* Indecent: Not decent
* Independent: Not dependent
* Indifferent: Not caring
* Ineffective: Not effective
* Inefficient: Not efficient
* Inflexible: Not flexible
* Informal: Not formal
* Inhabit: To live in a place
* Initial: At the beginning
* Inject: To introduce a liquid into something
* Injury: Harm or damage
* Injustice: Unfair treatment
* Inquisitive: Eager to learn or know
* Inside: Within something
* Insincere: Not sincere
* Insightful: Showing a deep understanding
* Inspect: To look at something carefully
* Inspire: To encourage or motivate
* Install: To put something in place
* Instant: Happening immediately
* Insure: To protect against risk
* Intact: Not damaged
* Intellectual: Relating to the mind
* Intelligent: Having a high level of intelligence
* Intention: A plan or purpose
* Interfere: To get in the way of something
* Internal: Inside something
* Internet: A global computer network
* Interrupt: To break in on something
This is just a small sample of the many words that start with "im" and "in". You can find many more by looking in a dictionary or online.
It's important to note that some words that start with "im" or "in" can have different meanings. For example, "immigrate" and "inhabit" don't necessarily mean "not." It's important to look at the context in which the word is used to determine its meaning.