How do you calculate atomic mass from an isotope?

Which of the following true? a_volcanoes and earthquakes often near the plate boundaries. b_volcanoes occur whereve there are tall mountains. c_earthquakes cause volcanoes in the same location to erupt violently d_volcanoes and earthquakes occur only where plates are colliding with each other

Acrystal that absorvd water from air is (blank)a. aqueousb. homogenousc. hygroscopicd. efflorescent

Nonpoint source pollution is difficult to control because it