  An element a in A_n, the Cayley-Dickson algebra is alternative if (a,a,x)=0
for all x. In this paper we characterise such elements for n>3.To do so,we
prove first the so called Yui's conjecture:For a and b pure elements in A_n. If
(a,x,b)=0 for all x then a and b are linearly dependent.Also we study
alternativity between every two elements and relate this with the norm of their
product .
