Question

e) the 4$^{th}$ period alkaline earth metal: symbol ​, name ​.

Explanation:

Step1: Recall periodic table structure

Alkaline earth metals are in group 2. Period 4 means the 4th row.

Step2: Identify element in group 2, period 4

Group 2, period 4 element is calcium? No, wait, period 4: let's list group 2 elements. Group 2: Be (period 2), Mg (period 3), Ca (period 4)? Wait, no, wait: period 1: H, He; period 2: Li - Ne; period 3: Na - Ar; period 4: K - Kr. Group 2, period 4: the element is Calcium? Wait, no, wait, group 2, period 4: atomic number. Be (4, period 2), Mg (12, period 3), Ca (20, period 4), Sr (38, period 5), Ba (56, period 6), Ra (88, period 7). Wait, so period 4, group 2 is Calcium? Wait, no, wait, period 4: the 4th period starts at K (19, group 1), so group 2, period 4 is Ca (20)? Wait, no, wait, maybe I made a mistake. Wait, alkaline earth metals are group 2. So period 4: elements from K (19) to Kr (36). Group 2: the second column. So K (1, period 4), Ca (2, period 4), Sc (3, period 4), etc. So Ca is group 2, period 4. Wait, but Ca is period 4? Wait, period 1: 1 - 2, period 2: 3 - 10, period 3: 11 - 18, period 4: 19 - 36. So Ca is 20, which is in period 4, group 2. So symbol is Ca, name is Calcium. Wait, but maybe I confused with Sr? No, Sr is period 5. Wait, let's check atomic numbers:

• Be: atomic number 4 (period 2)
• Mg: 12 (period 3)
• Ca: 20 (period 4)
• Sr: 38 (period 5)
• Ba: 56 (period 6)
• Ra: 88 (period 7)

So yes, period 4, group 2 (alkaline earth metal) is Calcium, symbol Ca.

Answer:

Symbol: $\text{Ca}$, Name: Calcium