HELP ASAP What did Dmitri Mendeleev contribute to science?
A. He discovered many unknown elements.
O B. He arranged the first periodic table.
O C. He developed the first atomic theory.
D. He developed the first model of the atom.

Which of these conditions most likely produces an unstable isotope?

Phosphorous can form an ion called phosphide, which has the formula p3−. this ion can form an ion called phosphide, which has the formula p3−. this ion properties very similar to those of pforms when a phosphorus atom loses three protonsis called a cationcontains 18 electrons

Which of these statements best explains why space exploration should be encouraged? it prepares humans to live without oxygen. it dispel myths about objects in space. it prevents comets and asteroids from striking earth. it creates technology to absorb harmful radiations in space.