Answer:
The correct option is: provide a source of counterions to prevent the build-up of charge at both the cathode to the anode.
Explanation:
A salt bridge is a U-shaped glass tube that is used in a voltaic cell or galvanic cell to connect the oxidation and reduction half-cells and complete the electric circuit.
<em>It allows the ions to pass through it, thus preventing the accumulation of charge on the anode and cathode as the chemical reaction proceeds.</em>
<u />
Therefore, the correct option is: <u>provide a source of counterions to prevent the build-up of charge at both the cathode to the anode.</u>
HClO, perchloric acid is a weak acid. Unlike strong acids like HCl or H2SO4 it not dissociate completely but partially such that an equilibrium exists between the dissociated ions and the undissociated acid. The equilibrium is as shown below:
HClO + H2O ↔ H3O⁺ + ClO⁻
Since HClO is a weak acid, the reverse reaction is favored over the forward reaction. Thus apart from water, HClO will be present in large amounts.
Radon is the heaviest gas on Earth with a density of about 9.73 g/L. This is very high actually.
For more informations, radon is mostly used in radioactivity and cancer therapy.
Hope this Helps :)
Answer : The formula of the missing product is, 
Explanation :
The given incomplete equation representing a reaction,

When the sodium metal react with the water then it gives a colorless solution of sodium hydroxide and hydrogen gas. In the solution, sodium hydroxide is present in the form of ions i.e,
and
ions.
The balanced chemical reaction will be,

Therefore, the formula of the missing product is, 
Because the easier a metal donates an electron (Low Ionization Energy), the more readily a non-metal with high electromagnetically will accept it.
Thus they match well, - one readily donates, the other readily accepts. This is how ionic bonding occurs.
Hope this helps.