Is Nikolaev Russian?

The Russian name, Никола́ев, transliterates as Nikolaev or as Nikolayev.

Which country is Mykolayiv?

Mykolayiv, Russian Nikolayev, also spelled Nikolaev, city, southern Ukraine. The city lies along the estuary of the Southern (Pivdennyy) Buh River, about 40 miles (65 km) from the Black Sea.