Nyob rau hauv lub neej niaj hnub no, tib neeg yuav tsum tau siv ntau cov khoom iav hauv lawv lub neej txhua hnub, tau ua tiav tsis tuaj yeem tshem cov iav. Cov iav muaj cov khoom ruaj khov, muaj zog tiv taus acid thiab alkali, thiab yog ib qho nyuaj thiab ruaj khov. Nws yog ib qho ntawm cov khoom siv raw rau cov khoom siv tseem ceeb tshaj plaws. Yog xav paub ntxiv