The pie chart displays population differences between Yemen and Italy in 2000 and 
the 
their probability in 2050
In general, both Remove the article
apply
country
 experienced big changes in all of the ranges. Change to a plural noun
countries
Yemen
 population of youngsters Change noun form
Yemen's
decrease
 one Wrong verb form
decreased
third
 Correct your spelling
one-third
while
 Italy lost only Linking Words
small
 portion of it. But it is a completely different case for Correct article usage
a small
middle
 range, YemenAdd an article
the middle