Thank you for the lecture sir really great but I have 1 doubt if the normal level of ppm is 1 then why r we adding 4 to 5 ppm and all in school water fluoridation
@bloomingheart6769
3 жыл бұрын
Thanks alot i was facing problem wit calculation of ppm ...im happy i learnt it here......so happy.😍😍😍
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