Why is the wave nature of a baseball not readily observable?

The wavelength of a baseball is extremely small due to its mass.

What is the significance of the Heisenberg uncertainty principle in the context of electron behavior?

It states that the more accurately we know an electron's position, the less accurately we know its momentum, and vice versa.

Because electrons exhibit wave-particle duality, meaning they possess properties of both particles and waves.

I can determine the electron configuration of an element using quantum numbers.

1
De Broglie suggested that if waves can behave like particles, then particles must also behave like waves, meaning all matter has a wavelength.
2
Schrödinger developed quantum mechanics to describe the wave mechanics of the electron, leading to the understanding that electrons exist as a cloud of probability density.
3
Heisenberg's uncertainty principle states that the more we know about an electron's location, the less we know about its momentum, and vice versa, which is an inherent quality of the electron.