Question

It is the of an element which
decides the group and the period of
an element in which it is to be placed.
1 Atomic mass
2 Atomic number
3 Electronic configuration
4 Valence electron​

Answer 1

Explanation:

the answer is electonic configuration for period number and valence electrons for period number.

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Answer 2

Answer:

Electronic configuration.

Explanation:

As any element for example Oxygen. With atomic number 8.has configuration like.

1s^2, 2s^2 2p^4.

Here the shell number that is "2 in this case" represents the period number. And the valence electron which is above the last shell names "s, p, d, f, and valence electrons here are 2,4) by adding them we get the group number.

So, here Oxygen is placed in 2nd period and 16th group(as P block element's group is calculate by adding the valence electron + 10)