Question 9 rank the effective nuclear charge z * experienced by a valence electron in each of these atoms:

Effective nuclear charge is the net positive charge felt by electrons.

The effective nuclear charge has a trend that follows in the periodic table. Across the period due to the constant electron shielding, the effective nuclear charge increases.  

For the trend the effective nuclear charge down the group, there is a decrease in the Z. For example in period: K, Ca, Sc, Ti.

The order will be: K<Ca<Sc<Ti.

In row, Na, K, Rb, Cs.

The order will be: Na>K>Rb>Cs.

For more information about the effective nuclear charge, refer to the link:

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8 carbon atoms forming single bonds with 18 hydrogen atoms; a triple bond exists between the third and fourth carbon atom from the right

explanation:

the answer would be b i believe