Learn Icelandic: Það er einn af vísindamönnunum hér inni. - There is one of the scientists in here.

The number one (einn) has to match the gender of the noun it represents in the group. Since it stands for one of the scientists, and vísindamaður (scientist) is a masculine noun, einn must take the masculine nominative form.

Why is the noun after af in the dative case?

The preposition af always triggers the dative case. In these partitive phrases meaning one out of a larger group, you will always use af followed by the dative plural form of the noun.

Why is there an ö in vísindamönnunum?

The singular root word is vísindamaður (scientist). In the dative plural, the suffix is -um, which triggers a vowel shift called the u-shift. This changes the a to an ö, giving us vísindamönnum. Finally, we attach the dative plural definite article -num to get vísindamönnunum.

Why do we use hér inni instead of hér inn?

The adverb inni describes a static location, meaning the subject is already inside. The word inn implies movement or direction, like walking into a room. Because the scientist is simply located in the room, we must use the static form inni.