"M" I believe is the symbol for molarity.
Ni solution could be used to remove lead from lead (II) nitrate.
Explanation:
The removal of lead from lead nitrate will take place by displacement reaction.
In displacement reaction less reactive element is displaced by more reactive element form it compound.
The reactivity is decided by the placement of metal in the activity series.
A metal which is at higher position in the activity series will be able to displace the metal or element having lower position.
From the options given we will check their position in the activity series in comparison to Pb
Cu is lower in series than Pb hence cannot displace.
Hg is placed lower in the series than Pb hence cannot displace Pb.
Ag is placed lower than Pb in the series hence cannot displace Pb.
Ni is placed above the Pb in activity series hence can displace lead.
Answer : The mass of chlorine reacted with the phosphorus is, 53.25 grams.
Explanation :
First we have to calculate the moles of phosphorus.
Now we have to calculate the moles of 
The balanced chemical reaction is:
From the balanced chemical reaction, we conclude that
As, 2 moles of phosphorous react with 3 moles of
So, 0.5 moles of phosphorous react with 
moles of
Now we have to calculate the mass of
Molar mass of = 71 g/mol
Therefore, the mass of chlorine reacted with the phosphorus is, 53.25 grams.
