String data type can store from zero to . . . . . . . . Unicode characters.

The correct answer is: B. 2 billion

A string data type can store from zero to 2 billion Unicode characters. A Unicode character is a unit of text that can be represented by a unique code point. The Unicode Standard defines a large repertoire of characters that can be used to represent text in any language.

Option A is incorrect because it is too small. A string data type can store more than 2 million characters.

Option C is incorrect because it is too large. A string data type cannot store more than 2 billion characters.

Option D is incorrect because it is too small. A string data type can store more than 1 million characters.