The question is incomplete.
The complete question probably is
The pH scale for acidity is defined by pH = − log₁₀[H⁺] where [H⁺] is the concentration of hydrogen ions measured in moles per liter (M). A solution has a pH of 2.55. Find the hydrogen ion concentration.
Answer: -
0.003 M
Explanation: -
pH = − log₁₀[H⁺]
Thus the hydrogen ion concentration [H⁺] = 
= 
= 0.003 M
Chemical Compound- a chemical substance consisting of 2 or more different chemically bounded chemical elements with a fixed ratio determining the composition. It is commonly used for electricty
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.
Bonding between 2 hydrogen atoms is 'covalent bond'.
Hope this helps you.
