Animated Solution for Chemistry - s and p-Block Elements: The metal used for making X-ray tube window is

Imagine the inner workings of an X-ray tube. Inside this high-energy environment, electrons are accelerated to massive speeds and smashed into a metal target to produce X-rays.

Once these X-rays are generated, they need a way out of the tube to be useful for imaging or scientific study. This exit path is provided by the X-ray tube window.

The material chosen for this window has a very specific and critical job: it must be highly transparent to X-rays, allowing them to pass through without absorbing them or interacting with them.

What happens if the X-rays interact with the window material? High-energy X-ray photons pack a serious punch. If they strike an atom, they can easily knock out its electrons.

This process is known as ionization. If the window material gets ionized, it will release a shower of stray electrons. These secondary electrons would create unwanted background noise and interference, completely ruining the precision of the X-ray study.

To prevent this, we need a material that holds onto its electrons with an iron grip. In chemical terms, the material must possess a very high Ionization Energy ($IE$).

Let's evaluate our given options: Sodium ($\text{Na}$), Beryllium ($\text{Be}$), Magnesium ($\text{Mg}$), and Calcium ($\text{Ca}$).

We know that Ionization Energy is inversely proportional to atomic size. As we move down a group in the periodic table, the atomic size increases, and the valence electrons get further away from the attractive pull of the nucleus.

Among the given metals, Beryllium is located at the very top of Group 2. It has the smallest atomic radius. Because of this compact size, its valence electrons are held extremely tightly by the positively charged nucleus.

But size isn't the only factor working in Beryllium's favor. Let's look at its electronic configuration.

Beryllium has an atomic number of $4$, which gives it a configuration of $1s^{2}2s^2$. Notice the outermost shell: the $2s$ subshell is completely filled.

In quantum mechanics, fully filled subshells offer exceptional stability. Removing an electron from this stable $2s^2$ state requires a massive amount of energy.

Combining its incredibly small atomic size with its highly stable electronic configuration, Beryllium boasts the highest Ionization Energy among the choices provided.

The high-energy X-rays simply do not have a high probability of ionizing it. Furthermore, its low atomic number ($Z=4$) means it absorbs very few X-rays, making it highly transparent.

Therefore, Beryllium is the undisputed champion and the perfect material for making X-ray tube windows. The correct option is (b).