Which ion is a polyatomic ion?

NH4+
Cl−
Ca2+
F−

Water, 35 liters. Carbon, 20 kilograms. Ammonia, 4 liters. Lime, 1.5 kilograms. Phosphorous, 800 grams. Salt, 250 grams. Saltpeter, 100 grams. Sulfur, 80 grams. Fluorine, seven-point-five. Iron, five. Silicon, three grams. And trace

amounts of 15 other elements.

the ingredients of the average adult,right down to the last specks of protein in your eyelashes. And even though science has given us the entire physical breakdown, there's never been a successful attempt at bringing a human to life. There's still something missing. Something scientists haven't been able to find in centuries of research. ...and in case you're wondering, all those ingredients can be bought on a child's allowance. humans can be made rather cheap. There's no magic to it.

metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

if it's not useful, feel free to report for mistake in answer.

the answer is d. 74.02