A fictitious element X is composed of 10.0% of the isotope X-55, 20.0% of the isotope X-56, and 70.0% of X-57. Calculate the average atomic mass of element X

Which description best characterizes the motion of particles in a solid?

What type of chemical bond is formed between two atoms of bromine 1. metallic 2. hydrogen 3. ionic 4. covalent

Robert leaves a chocolate bar in his car while attending school all day. when he goes to his car in the afternoon, the bat has changed into gooey liquid. what happened to the chocolate bar