Answer:
(a)
![^(23)_(11)Na](https://img.qammunity.org/2020/formulas/chemistry/college/ttu4uj5outv3jqrcxgn86366ywgl6yvgqk.png)
(b)
![^(64)_(28)Ni](https://img.qammunity.org/2020/formulas/chemistry/college/7312l4sal9vtgg4xa9sgr8ivnvzi3j9omh.png)
(c)
![^(115)_(50)Sn](https://img.qammunity.org/2020/formulas/chemistry/college/rui2sk89cml24bq6d81i5y1eg04singm0w.png)
(d)
![^(42)_(20)Ca](https://img.qammunity.org/2020/formulas/chemistry/college/dcxhl9nugpanuujnbgr9use3y6jholzezh.png)
Step-by-step explanation:
Hello,
In this case, Z stands for the isotope's atomic number and A for the isotope's atomic mass, in such a way, looking for each isotope one concludes that the proper symbol, in the form of
turn out being:
(a)
![^(23)_(11)Na](https://img.qammunity.org/2020/formulas/chemistry/college/ttu4uj5outv3jqrcxgn86366ywgl6yvgqk.png)
(b)
![^(64)_(28)Ni](https://img.qammunity.org/2020/formulas/chemistry/college/7312l4sal9vtgg4xa9sgr8ivnvzi3j9omh.png)
(c)
![^(115)_(50)Sn](https://img.qammunity.org/2020/formulas/chemistry/college/rui2sk89cml24bq6d81i5y1eg04singm0w.png)
(d)
![^(42)_(20)Ca](https://img.qammunity.org/2020/formulas/chemistry/college/dcxhl9nugpanuujnbgr9use3y6jholzezh.png)
Best regards.