What is the shortcut key to subscript selected words in MS-Word?

In MS Word, you can format text using shortcut keys:
Ctrl + = → Subscript
This lowers the selected text slightly below the baseline.
Example: H₂O (the "2" is subscript).
Ctrl + Shift + = → Superscript
This raises the selected text slightly above the baseline.
Example: X² (the "2" is superscript).
Ctrl + - → Not assigned for subscript formatting.
Ctrl + Shift + - → Used for applying a hidden character formatting or removing hyphenation, not for subscript.
Therefore, the correct shortcut key to apply subscript in MS Word is Ctrl + =.