I'm studying both traditional and simplified characters. In tone practice, when 困难 pops out the "correct" tone for the second char is neutral. When 困難 appers, it says it should be a 2nd tone.
Which one is correct?

Oops, they should be the same. The official mainland version has a neutral tone, but perhaps in Taiwan it's a second tone--does anyone know? I can have it accept either if so.

Second tone is correct.

Okay, I'll have that go live later today. Thanks!

For the mainland, according to 普通话 水平 测试 实施 纲要，the light tone is optional, it can be pronounced as a neutral tone or a second tone.

In Taiwan, according to the online dictionary provided by the education department, it is a neutral tone. http://dict.revised.moe.edu.tw/cgi-bin/newDict/dict.sh?idx=dict.idx&cond=%A7x%C3%F8&pieceLen=50&fld=1&cat=&imgFont=1

Doh! It's such a headache when the sources disagree. I'm never sure if the tone is really supposed to be pronounced or if the source author just got lazy and stuck it in without checking. Googling around gave about half-and-half 2nd vs 5th. I'll check with a primary source, but it might take a while.

For the mainland, according to both 汉英大辞典 and 精选汉日辞典 the 难 should be pronounced with a neutral tone.

普通话 水平 测试 is the Putonghua proficiency test for the native Chinese, and attaining a certain level in this test is the prerequisite for applying for any job as a broadcaster, teacher or government official. 普通话 水平 测试 实施 纲要 is the syllabus for those preparing for this test. It lists the pronunciations of about 17,000 words. There is also a list of 546 words that must be pronounced as neutral tone. Any word not found in this syllabus (实施纲要), should be pronounced as it is listed in the dictionary 现代汉语辞典。Because of the importance of this proficiency test, this 实施纲要 and the 现代汉语辞典 together have become the de facto standard for the Putonghua pronunciation in the mainland, and their authority just can’t be matched by any other dictionary, text book or professor.

This syllabus, which comes with 2CDs containing the pronunciations of all those 17,000 words can be obtained from amazon.cn for ￥32.60, which is less than US$5.0. So, would Skritter consider obtaining a copy and stop any further arguments about the neutral tones?

http://www.amazon.cn/%E6%99%AE%E9%80%9A%E8%AF%9D%E6%B0%B4%E5%B9%B3%E6%B5%8B%E8%AF%95%E5%AE%9E%E6%96%BD%E7%BA%B2%E8%A6%81-%E5%9B%BD%E5%AE%B6%E8%AF%AD%E8%A8%80%E6%96%87%E5%AD%97%E5%B7%A5%E4%BD%9C%E5%A7%94%E5%91%98%E4%BC%9A%E6%99%AE%E9%80%9A%E8%AF%9D%E5%9F%B9%E8%AE%AD%E6%B5%8B%E8%AF%95%E4%B8%AD%E5%BF%83/dp/B00116NDWE

According to my primary source, it is 2nd tone.

That sounds like a great resource, pts! I'll see about ordering a copy tomorrow.

I'd love if it was totally authoritative, but it seems like nothing ever quite stops all argument, because there's always more regional variations. We'll surely support the mainland standard, but when possible we also gotta do right by our Taiwanese 朋友, sometimes even when the MOE doesn't support it.

It is definitely neutral tone. I have checked with a few friends who have standard pronounciation in China. 2nd tone is not even optional in mainland China, they consider it as wrong.

One feature that the 实施纲要 will help in this neutral tone problem is that it distinguishes the neutral tones between mandatory and optional ones by adding a dot before those that are optional. For example, since 北边 is optionally neutral, so its pinyin is shown as “běi•biān”, with a dot before biān and “biān” is still marked as first tone.