What is the number one ”most serious problem” considered by half of the world's population?

More than half of the world's people consider the gap between rich and poor to be the most serious problem in their country.
A public opinion survey conducted by the Pew Research Center last spring targeting citizens of 36 countries revealed that 54% of respondents recognized the "inequality between rich and poor" as the most serious problem in their country, and 54% of respondents considered it to be somewhat serious.
The survey found that the largest proportion of respondents in EU member states such as Germany (92%), Turkey (92%) and Greece (91%), as well as Argentina (91%),
% of respondents in developing countries such as the United States and the United Kingdom also see the gap between rich and poor as a major problem.
"The gap between rich and poor is becoming a growing problem," he explained. South Korea's figure was 82%, which was similar to other countries such as Australia (82%), the United States (83%), and Japan (80%).
Among South Korean respondents, 47% said the gap between rich and poor was a "very big problem," while 35% said it was a "somewhat big problem."