Which has highest $$pH?$$

Solution :
$$pH = {\text{log}}\frac{1}{{\left[ {{H^ + }} \right]}}$$
$$pH$$  is inversely proportional to hydrogen ion concentration. As concentration of $${H^ + }$$ decreases $$pH$$  increases and vice-versa.
Ammonium chloride $$\left( {N{H_4}Cl} \right)$$   is a salt of weak base and strong acid. So, its aqueous solution will be acidic as
$$N{H_4}Cl + {H_2}O \to \mathop {N{H_4}OH}\limits_{{\text{Weak base}}} + \mathop {HCl}\limits_{{\text{Strong acid}}} $$
So, $$pH$$ of $${N{H_4}Cl}$$  is less than 7.
Sodium nitrate $$\left( {NaN{O_3}} \right)$$   is the salt of strong acid and strong base. So, its aqueous solution is neutral as
$$NaN{O_3} + {H_2}O \to \mathop {NaOH}\limits_{{\text{Strong base}}} + \mathop {HN{O_3}}\limits_{{\text{Strong acid}}} $$
So, $$pH$$ of $${NaN{O_3}}$$  is 7.
Potassium acetate $$\left( {C{H_3}COOK} \right)$$   is a salt of strong base and weak acid. Its aqueous solution will be basic and $$pH$$  value will be greater than $$7 \approx 8.8$$
$$C{H_3}CO{O^ - }{K^ + } + {H_2}O \to \mathop {C{H_3}COOH}\limits_{{\text{Weak acid}}} + \mathop {KOH}\limits_{{\text{Strong base}}} $$
Sodium carbonate $$\left( {N{a_2}C{O_3}} \right)$$   is a salt of strong base and weak acid. Its aqueous solution is also basic and its $$pH$$  value will be more than 10,
i.e. highest among them.
$$N{a_2}C{O_3} + {H_2}O \to \mathop {2NaOH}\limits_{{\text{Strong base}}} + \mathop {{H_2}C{O_3}}\limits_{{\text{Weak acid}}} $$