Yes, China has a larger population, meaning more economic and military potential.
No, China has the numbers, but they lack the means to overcome the United States anytime soon.
Economically, absolutely, although this really isn't surprising or our fault, as some would suggest. China has already passed us as the world's largest trading nation and as the nation with the world's largest purchasing power parity. They won't pass us in total GDP for some time (perhaps 20 years or so), but, at any rate, they will pass us. The reason for this is quite simple, and it is the reason for pretty much every gain that China has ever had: it has a metric assload of people. More people equals more people to tax and to buy things. The only reason that we've been so far ahead of them for the past few centuries (a mere blip in the historical timeline) is because we've been more advanced and less isolationist, but with China embracing capitalism and civil rights more and more lately, their economy has been flourishing and advancing, and the country's sheer manpower is enough to eventually propel it into superpower status. Now, that is, again, economically speaking, and for a long time after China gains economic superiority, the U.S. will continue to be the word's cultural, military, and political hegemon. I mean, Britain remained so until the end of WWII or, arguably, the early 1950's, even though the U.S. had had a larger economy since perhaps as early as the 1880's. Inevitably, though, the U.S. will recede, just as all nations do. China is no exception either, and its One Child policy will only accelerate its decline. I have a theory on what specifically makes nations rise and fall, but this comment is running long, so I can message anyone if they're interested. Suffice to say that I think India will probably overtake China's population and economy a few decades after China overtakes the U.S.'s economy.
They'll certainly pass the USA regarding GDP. In other aspects, i'm not so sure.
GDP wise, maybe but I still think the U.S economy will manage for quite a long time. Militarily wise, it's pretty much impossible. The U.S is decades ahead of China in national defense.
I read somewhere a year or two ago that China is about to have a major clean water problem but I can't remember where I got this info so I don't know if I can trust it's validity