Which of the following substances is an element? A. water B. table salt C. iron oxide D. hydrogen

Explanation:

An element has a uniform composition, cannot be broken down by chemical change, every atom has the same atomic number, and can be found on the Periodic Table.

Water is made of hydrogen and oxygen atoms (H₂O) so it is not an element.

Table salt is made of sodium and chloride atoms (NaCl) so it is not an element.

Iron oxide is made up of iron and oxygen atoms, so it is not an element.

Hydrogen is an element. It can be found on the Periodic Table as element H.

The correct answer is D. Hydrogen

question: ray weighs 100 kilograms, his wrestling partner, bobby, weighs 50 kilograms. if ray moves at 4 m s , how fast will bobby have to run at him to apply an equal amount of kinetic energy?

answer: 8 m/s he needs to run twice as fast to keep up so he has some work to do

explanation:   if the mass has units of kilograms and the velocity of meters per second, the kinetic energy has units of kilograms-meters squared per second squared.

question answered by

(jacemorris04)

aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.