お〜・ご〜 (polite prefixes)
(polite prefix)
お + Japanese-origin noun · ご + Chinese-origin noun
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お and ご in front of a noun make it polite. お usually goes with native Japanese words (お茶, お金, お名前, お水), and ご with words of Chinese origin (ご家族, ご両親, ご飯, ご住所).
Some words almost always have their prefix, even in casual speech: お茶, お金, ご飯, お風呂, お手洗い.
With other people's things, it shows respect: お名前は何ですか, "what's your name?"; ご家族は何人ですか, "how many are in your family?" You don't use it for your own family or things, except for words that always take it.
There are exceptions to the rule (お電話, お時間 use お with Chinese-origin words), so learn common ones as whole words.
Examples
お茶を飲みませんか。
Would you like some tea?
ご家族は何人ですか。
How many people are in your family?
お名前は何ですか。
What's your name?
ご飯を食べましょう。
Let's eat.
お金がありません。
I don't have any money.