Floating point normalised numbers in binary
I'm assuming you're talking about IEEE754. Unless I'm missing something, your book is wrong.

Every number in IEEE754 is represented as normalized (starting with a 1), unless your number is subnormal. A number is only subnormal if the mantissa is minimal (all zeroes). Since the first bit is the sign bit, $10$ could be the start of a subnormal number.

For example $10000000000000000000000000000001$ is the subnormal number $-2^{-149}$.