A key signature is the collection of flats and sharps sign at the beginning of each staff. There are fifteen major key signatures and are grouped into three namely:
Natural key – 1 key
Sharp keys – 7 keys
Flat keys – 7 keys
Natural key: the natural key has no sharp or flat sign. The staff has no accidental at its entrance. The key is C major as shown below

Sharp keys: there are seven sharp keys. They are
Name of key
Number of sharps

G major
1 – F

D major
2 – F C

A major
3 – F C G

E major
4- F C G D

B major
5- F C G D A

F# major
6 – F C G D A E

C# major
7- F C G D A E

Gmajor Dmajor Amajor Emajor Bmajor F# C#

Flat keys: there are also flat keys. They are:

Name of key
Number of flats

F major
1- B

Bb major
2- B E

Eb major
3- B E A

Ab major
4 -B E A D

Db major
5- B E A D G

Gb major
6- B E A D G C

Cb major
7- B E A D G C F

F          B            E          A             D          G       C   

What is key signature?
Which key is natural?
G major has how many sharp?
How many keys are in sharp series