Why did the Mars Climate Orbiter crash?

Ahypothrticalax type of ceramic material is known to have a density of 2.10 g/cm3 and a unit cell of cubic symmetry with a cell edge length of 0.57 nm. the atomic weights of the a and x elements are 28.5and 30.0 g/mol, respectively. on the basis of this information, which of the following crystal structures is (are) possible for this material: sodium chloride, cesium chloride, or zinc blende

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!

Compare and contrast the bohr model and the electron cloud models of the atom.