Select the elements that have 4 valence electrons. hydrogen (H)

krypton (Kr)

strontium (Sr)

carbon (C)

oxygen (O)

tin (Sn)

What are antigens and antibodies? how are they involved in the body’s response to incompatible blood?

Which pair of sentences is describing the same velocity? a. a car is parked. a car is moving in circles. b. a bus drives 40 miles per hour north. a truck drives 50 miles per hour north. c. a boy walks east at 6 kilometers per hour. a girl walks west at the same speed as the boy. d. valerie rides her bike south at 8 kilometers per hour. owen jogs south at 8 kilometers per hour.

Use the drop-down menus to match each part of the scenario to the correct scientific practice. akira records the speed of a reaction without a catalyst and then with a catalyst. akira creates a reaction without a catalyst and repeats the reaction with a catalyst. akira turns in a written lab report to his science teacher. akira wonders, "will adding a catalyst speed up this chemical reaction? " akira writes in his notes that adding a catalyst sped up the chemical reaction because the catalyst lowers the activation energy needed to get the reaction started.