By age 3 years old most 3 year olds know at least 200 words.
However some 3 year olds know more than 200 words and have a vocabulary of 250 to 300 words but most 3 year olds know at least 200 words.
As the 3 year old gets older they start learning more words and their vocabulary gets even better.
But all kids are different so if your 3 year old does not know at least 200 words it doesn't mean there is anything wrong with them.
Some kids know more words than others which is normal and as long as you teach the kid to read and teach them words then they will usually eventually learn the words.