Once you have filled in all the gaps on a separate sheet of paper, enter the four missing element symbols in the first r

[answerhappygod]

Once you have filled in all the gaps on a separate sheet of
paper, enter the four missing element symbols in the first row of
the table into the answer box below. You can open the first hint to
view a video that steps you through filling in the first column of
the table.
Enter the four missing symbols for the first row of the table
from left to right, separated by commas, into the answer box
below.
Use the stacked super/subscripts button (available in the
templates button menu above the answer entry box) to enter the
symbols in the following form: mass numberatomic number a t o m i c
n u m b e r m a s s number Symbol, or for example 1735Cl
.Please help