Question

how many electrons can be placed in 3d orbital?

Answer 1

We each orbital can occupy maximum number two electrons.

Once we know the number of obital in given subshell then we can find the number of electrons.

For that we can use following triangle.

l       orbital                        possible value of mL                               Number of max orbital

0        (s)                                            0                                                             1

1         (p)                              -1        0           +1                                              3

2         (d)                          +2 -1       0     +1    +2                                            5

So d orbital has 5 orbitals and each orbital contains 2 electrons.

So the number of electrons in d oribtla = 5 x 2 = 10