Question

What is the correct grammar/punctuation for saying. “Thank you”?

Answer 1

Hint: According to studies, the simple act of saying "thank you" will lead to a happier life. When you show gratitude to others, it not only makes them happy, but it also makes you happy. It brings inner pleasure and peace of mind.

Complete answer:
If you want to include someone's name after "thank you," put a comma after "thank you" to distinguish the statement from the addressee's name. If the sentence continues after the word, add another comma to distinguish it from the rest of the sentence.

The name would be in the vocative case if it were Latin. The person being addressed is placed into the "case of address" in English, but the case of address looks just like a normal word in English since case endings have mostly been lost (except for pronouns).

Here are a few examples.
“Thank you, Kavya.”
“Thank you, for all your hard work.”
“Thank you, Sonali, for fixing my flat tire.”
“Thank you, Mahi, for putting in such extraordinary efforts at the state swim meet!”
“Thank you, Kiara, for spending time with me yesterday.”

There's no right or wrong way to punctuate "Thank you"; you can use a period "." or an exclamation point "!" (as long as you don't use a question mark). It's mostly a matter of personal opinion based on what you're trying to say as the author. If you're trying to express enthusiasm, I'd go for an exclamation point (though you might use a period if you prefer). I'd use a pause if you're trying to be polite (as in business writing), the character is trying to be sarcastic, or they're deadpanning their speech.

Note: English Phrases to Use When Saying "Thank You". There is no need to be concerned, don’t bring it up, Anytime, I'm happy to assist, You're welcome, No problem, No worries, Don't mention it, My pleasure, Anytime, It was the least I could do, Glad to help.