Coal Tar. Tar derived from both coal and wood (e.g., juniper, pine) are both used for medicinal purposes. However, coal tar is the type used most commonly to treat psoriasis. Tar can help slow the rapid growth of skin cells and restore the skin's appearance. In addition, it can help reduce the inflammation, itching and scaling of psoriasis. Tar products can vary dramatically from brand to brand.
Quick Answer. The lightest element on the periodic table is hydrogen. The atomic weight of hydrogen is 1.00794 and the atomic number is 1. Hydrogen is the most abundant element on the periodic table with 75 percent of the mass of the universe consisting of hydrogen. Continue Reading.
The noble gases (arranged in order of increasing atomic weight) are helium, neon, argon, krypton, xenon and radon. Helium, neon and argon are the three noble gases with the lowest atomic masses. Helium, Neon, Argon. Helium, neon, and argon are the three lightest members of the noble  gases. Hydrogen is the lightest of all elements. According to the Periodic  Table, its atomic weight is 1.00794 u, even lighter than helium.