Boron' occurs in nature in the form of two isotopes '_5^(11)B' and '_5^(10)B' in ratio of 81 and 19 respectively. Calculate its average atomic máss.

Naturally occuring boron has two isotopes of masses 10 amu and 11 amu. Calculate the percentage of each isotope if the average atomic mass of boron is 10.2 .

Naturally occuring chlorine is a mixture of two isotopes. In every sample of this element 75.77% of the atoms are 35Cl and 24.23% are atoms of 37Cl. The accurately measured atomic mass of 35Cl is 34.9689 u and that of 37Cl is 36.9659 u. From these data. Calculate the average atomic mass of chlorine.

A chemical reaction 2A rarr 4B +C in gas phase occurs in a closed vessel the concentration of B is found to increase by 2.5 xx10^(-3) mol L^(-1) in 5 second calculate (i) the rate of appearance of B (ii) the rate of disappearance of A