How did Mendeleev know that there must be undiscovered elements and how did he take this into account when he designed his periodic table?

The is a particle with one unit of positive charge a. proton b. positron c. electron d. nucleus awnser quick it is a important science test!

To prevent the presence of air, noble gases are placed over highly reactive chemicals to act as inert "blanketing" gases. a chemical engineer places a mixture of noble gases consisting of 4.37 g of he, 13.36 g of ne, and 36.65 g of kr in a piston-cylinder assembly at stp. calculate the partial pressure in torr of kr.

What is the reaction between an acid and a base