What is the leading tone in C Major? To answer this question, we first need to understand what C is, what a major scale is, and what a leading tone is.
1. C is a fundamental pitch in the musical system of 88 notes, divided into 9 groups, with seven complete groups. The first note of these seven complete groups is named C. The last group contains only one note, also named C, specifically the C in the fifth octave, which can be referred to as C8 if we use the grouping method from group 0 to group 8.
2.
A major scale, also known as the natural major scale, consists of seven notes, which are marked with Roman numerals as follows:
Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ Ⅵ Ⅶ
These seven notes, along with the octave of the tonic, make a total of eight notes. The relationship between each pair of adjacent notes is:
Whole Whole Half Whole Whole Whole Half
This can be summarized in the following diagram (natural major scale):
3.
The various degrees in the natural major scale are referred to as scale degrees, and the names of these degrees in the natural major scale are shown in the following diagram:
From the diagram above, we can see that the leading tone is to the left of the tonic in the natural major scale.
Thus, the natural major scale with C as the leading tone is as follows (the diagram is based on the grouping method from group 0 to group 8):
It can be seen that the tonic is 
. It is evident that in the natural major scale, C is the leading tone.
Please see what key the following piece of music is in:
Reference:What is D minor