Guess what letter conforming each word

Question

^{This is an entry in the Fortnightly Topic Challenge #41: Short and Sweet.}

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1 letter only could be mean anything.

With an additional letter in front, could be used as medicine component and something you definitely learn or at least heard once.

Add another letter in front, you would possibly hear that many times.

Add an additional letter in front, you would found an independent country.

With an additional letter, in the end, you would found something related to apple.

Add another letter in the end, you would found something bad.

Hint:

Each letter is unique.

Answer 1

1 letter only could be mean anything.

I - which is also the Roman numeral symbol for 1.

With an additional letter in front, could be used as medicine component and something you definitely learn or at least heard once.

Li - chemical symbol for Lithium, which most people have seen on the periodic table.

Add another letter in front, you would possibly hear that many times.

Ali - Many people have that name, e.g, Muhammad Ali,

Add an additional letter in front, you would found an independent country.

Mali

With an additional letter, in the end, you would found something related to apple.

Malic - the acid was first isolated from apple juice.

Add another letter in the end, you would found something bad.

Malice