Answer: here are the four capitalization errors in the sentence "The lena River in russia flows Northeast nearly three thousand miles from it's Source in the mountains to the Artic ocean"
Explanation: "The" should not be capitalized. The article "the" is not a proper noun, so it should not be capitalized.
"russia" should be capitalized. The country "Russia" is a proper noun, so it should be capitalized.
"it's" should be "its". The possessive pronoun "its" should not have an apostrophe.
"Artic" should be capitalized. The ocean "Arctic" is a proper noun, so it should be capitalized.
The corrected sentence is:
The Lena River in Russia flows northeast nearly three thousand miles from its source in the Arctic Ocean.
I hope this helps!