(Quickly please) Sapphires and rubies are forms of the mineral corundrum. corundrum is one of the heardest known natural mayerials. the hardness of ionic compounds depends on the structure of the crystal and the strength of the ionic bonds. yhe distance between the aluminum ions and oxide ions is 191 pm. use coulombs law to explain how the bonding in influences its properties.

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later

Electrons are emitted

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The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.