Can all quartiles and deciles be expressed as percentiles? Explain?

Answer 1

yes, assuming you're asking about stats and particularly psychometrics.

the 1st quartile is 25%, the second is 50%, the third is 75% and the fourth is 1/1 or 100%

The deciles are the same but in 10ths. 1st = 10%, 2nd = 20% etc...

These quartiles and deciles represent a specific point on the scale, as such, they (as can all other results) be reported as a percentile of the total scale.