Calcium (atomic number 20) has electron configuration 1s2,2s2,2p6,3s2,3p6,4s2. the atomic number of scandium is 21. which orbital does the 21st electron enter? a.3d b.4p c.4d d.4f

If you look at the periodic table, you can see that Sc is in the transitional group metals, so it should have d orbital,
also it is in 4th period, so it has 3d orbital 
and 21 st electron enters 3d orbital
Answer a.3d
after 4s electrons go into 3d -orbital

Ithe undersigned only for use your own email and delete any and copies and of the itself and to be there is a good timewhat does a decrease in temperature indicate about the molecules in a sample of liquid water? decreased chemical energy of the moleculesdecreased kinetic energy of the moleculesincreased chemical energy of the moleculesincreased kinetic energy of the moleculeshow does a sample of helium at 15 â°c compare to a sample of helium at 215 k? the helium at 15 â°c has a higher average kinetic energy than the sample at 215 k.the helium at 15 â°c has lower nuclear energy than the sample at 215 k.the helium at 15 â°c has slower-moving atoms than the sample at 215 k.the helium at 15 â°c has smaller atoms than the sample at 215 k.

Answeropposite;