Arrange the following atoms according to decreasing effective nuclear charge experienced by their valence electrons: Cl, Na, P, and S. Rank from largest to smallest. To rank items as equivalent, overlap them. Cl Na P S
Largest Smallest

Cl < S < P < Na

Explanation:

We have to understand the trend for effective nuclear charge before answering the question;

The periodic table tendency for effective nuclear charge: Increase across a period (due to increasing nuclear charge with no accompanying increase in shielding effect). Decrease down a group (although nuclear charge increases down a group, shielding effect more than counters its effect).

Based on this, the elements can be arranged in the following order;

In decreasing order;

Cl < S < P < Na

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-