The above picture shows a type of igneous rock called obsidian. why is the top rock so shiny and smoother than the others?

The rock is shiny and smoother due to how it was formed and the composition.

Explanation:

Obsidian is an example of an extrusive igneous rock. They are categories as a volcanic glass family. The contents of obsidian is mostly silica(SiO2).

Like most extrusive igneous rocks , obsidian is formed when magma migrate to the earth surface as lava. This lava, due to the temperature on the earth surface it will solidify rapidly denying the rocks adequate time to form crystals.

Obsidian are majorly found in the area where volcanic activities is prevalent . The volcanic eruption releases the lava required for it formation to the earth surface . The reason for the top rock so shinny , glassy and smoother is the rapid cooling of the lava which denies the rock adequate time to form crystals. The inability of this crystal to grow gives the rock the shinny, glassy , smoother, and conchoidal fracture it possess.

Obsidian's are majorly black . Although they might possess other color like blue but it is rare . The picture above is an obsidian with a very smooth texture and glassy nature.  

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6