What is the difference between the words happy and sad in their formality?

Sure, here's the difference between the words happy and sad in their formality:

Happy:

• Formal: Happy is a positive adjective that expresses a state of emotional well-being or contentment.
• Examples: She was happy to receive the promotion, and she was happy to see her friends at her wedding.

Sad:

• Formal: Sad is an adjective that expresses a state of emotional distress or unhappiness.
• Examples: She looked sad when she realized she wouldn't be able to attend the party, and she cried when she heard the news of her friend's illness.

Note:

• In some formal contexts, "happy" can be used to express a state of superficial contentment or a lack of concern.
• In some other formal contexts, "sad" can be used to express a state of joy or amusement.