Now let's define range which a normalised mantissa can signify. Let's presume that our present representations has normalised mantissa so left most bit can't be zero so it has to be 1. So it's not required to store this first bit and it's being presumed implicitly for number. So a 23-bit mantissa can signify 23 + 1 = 24 bit mantissa in our representation.

So smallest mantissa value can be:

Implicit first bit as 1 followed by 23 zero's which is   

0.1000 0000 0000 0000 0000 0000

Decimal equivalent = 1 × 2^-1 = 0.5

Maximum value of mantissa:

Implicit first bit 1 followed by 23 one's which is 

0.1111 1111 1111 1111 1111 1111

Decimal equivalent:

For finding binary correspondent let's add 2^-24 to above mantissa as below   

Binary: 0.1111 1111 1111 1111 1111 1111