What is the electron configuration of an element with atomic number 20? a. 1s2 2s2 2p6 3s2 3p5 b. 1s2 2s2 2p6 3s2 3p6 c. 1s2 2s2 2p6 3s2 d. 1s2 2s2 2p6 3s2 3p6 4s2 e. 1s2 2s2 2p6

D.  The number of electrons equals the atomic number for a neutral element.  Each number after the letter refers to the number of electrons in that shell.  So for D, 2+2+6+2+6+2 = 20 electrons, which is equal to the atomic number.

D. 1s2 2s2 2p6 3s2 3p6 4s2

Hope this helps!

h let me think

(newtons first law)

conservation of momentum law states :

momentum before collision = momentum after collision

momentum p (kg-m/s)= mass * velocity

say moving car=1 000 kg, velocity = 10 m/s then p = 1 000*10= 10 000 kg-m/s

say still car = 2 000 kg, velocity = 0 m/s then p = 2 000* 0 = 0 kg-m/s

total momentum prior to collision = 10 000 + 0 = 10 000 kg-m/s

momentum after collision = 10 000 kg-m/s

mass now = 1 000 kg+2 000 kg = 3 000 kg

10 000 = 3 000 kg* velocity m/s

10 000/3 000 = velocity

3.33 m/s = velocity after collision

an impulse is a force applied over time , momentum is exclusive of external forces and a perfect collision is implied