Question

How many periods of the modern periodic table contain 18 elements only?​

Answer 1

Answer:

There are total 7 periods and 18 columns in modern periodic table.

only 1 period contains of 18 element ( period no. 4 to period no. 7 ) contains 18 elements

Answer 2

Answer:

There are seven periods in the periodic table, with each one beginning at the far left. A new period begins when a new principal energy level begins filling with electrons. Period 1 has only two elements (hydrogen and helium), while periods 2 and 3 have 8 elements. Periods 4 and 5 have 18 elements.

Explanation:

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