What is the last element in period 4?

The last element in period 4 of the periodic table is Krypton (Kr), which is a noble gas. Here is some information about Krypton:

1. Atomic Number: Krypton has an atomic number of 36, meaning it has 36 protons in its nucleus.

2. Symbol: The chemical symbol for Krypton is Kr, derived from its name.

3. Discovery: Krypton was discovered in 1898 by Sir William Ramsay and Morris Travers. It was identified as a new element in the residue left after evaporating liquid air.

4. Properties: Krypton is a colorless, odorless, and tasteless gas. It belongs to the noble gas group, which means it is very stable and unreactive due to its full outer electron shell. It does not readily react with other elements.

5. Abundance: Krypton is present in the atmosphere in trace amounts, making up about 1 part per million. It is obtained by fractional distillation of liquid air. It is also found in some minerals and meteorites.

6. Uses: Krypton is mainly used in lighting applications, such as high-intensity discharge lamps, fluorescent lamps, and flash lamps. It is also used in lasers, as an insulating gas in windows, and in some specialized photographic techniques.

7. Isotopes: Krypton has several isotopes, with Kr-84 being the most abundant natural isotope. Other isotopes, such as Kr-81 and Kr-85, are used in scientific research and medical imaging.

8. Noble Gas: Like other noble gases, Krypton is known for its low reactivity and stability. These characteristics make it useful in applications where a non-reactive gas is required.

In summary, Krypton is the last element in period 4 of the periodic table. It is a noble gas with a low reactivity, and it has various applications in lighting, lasers, and other specialized fields.