It's spelled Tajikistan. Also, the Marshalls and Micronesia technically "became" countries in 1986, when their Compacts of Free Association with the US went into effect (and they were consequently removed from US trust territory status). They only joined the UN in 1990. Perhaps this should be a quiz about countries that have joined the UN since that time.
It wouldn't accept Tajikistan, but I saw that there was one comment, so I clicked to see if it said anything about what the erraneous spelling was. It didn't, and instead I got spoiled by the Marshall Islands.
A lot of these were countries before but when the merged with an another they were no longer countries and so their independence would be when they returned back to normal as they were not that country for a long time.
Germany is not a new country. Modern day Germany is the same country as what was known as West Germany before. Both are the Federal Republic of Germany. East Germany joined the Federal Republic in 1990.