E-sharp.
The leading tone in the key of D, whether major or minor, is C#.
G sharp (enharmonic A flat).
The A harmonic minor scale uses 1 sharp on the seventh degree, that would be a G♯, and you play the G♯ both when ascending and descending. The sequence of tones and semitones in a harmonic minor scale are as follows: Tone Semitone Tone Tone Semitone, Tone-and a half, Semitone. In A minot this is A (up a tone), B (up a semitone), C (up a tone), D (up a tone), E (up a semitone), F (up a tone-and-a-half), G♯ (up a semitone), A.
to show light and shade, without it it would all be mono-tone and grey.
leading tone
The leading tone in a key is one half-step below the tonic. In the key of A major, the leading tone is G-sharp.
C is the leading tone in the Key of D.
The leading tone is one half-step below the tonic, so in the key of B-flat the leading tone is A.
The leading tone in a scale is one half-step below the tonic. In the key of C# major, the leading tone is B#.
C-sharp. The leading tone is one half-step below the tonic.
The leading tone is the seventh note in the scale. For D-flat major, this would be C.
resolution
The leading tone is the seventh scale degree of the diatonic scale which in F Major is the note "E".
E
E
leading tone