... trong bng HTTH ca nguyờn t nguyờn t cú 20n, 19p v 19e.Cõu 5: Bit rng khi lngmt nguyờn t oxi nng gp 15,842 ln v khi lng ca nguyờn t C nng gp 11 ,90 59 ln khi lng ca nguyờn t H. Nu chn 1/12 khi ... ca cỏc ng v (ng vi nguyờn t ú cú ba ng v).Cõu 2: Nguyờn t khi TB ca nguyờn t R l 79, 91. R cú hai ng v. Bit R 79 Z chim 54,5%. Nguyờn t khi ca ng v cũn li cú giỏ tr no?Cõu 3: nguyờn t khi TB ... v. Xỏc nh nguyờn t X, Y.Cõu 8: Ion X2- cú 10 electron. Ht nhõn nguyờn t X cú 9 notron. Vit kớ hiu ca X.Cõu 9: Nờu ng dng ca C146 ?Cõu 10: Oxit ng vi húa tr cao nht ca nguyờn t Y l YO3....