Identical Valency in Hydride and Higher Oxide:

To determine which of the 4th period elements exhibit identical valency in both its hydride and higher oxide, let's analyze each element: Br, Ge, As, and Se.

Br (Bromine):
- Bromine belongs to group 17, also known as the halogens.
- The valency of halogens is typically -1, as they have a tendency to gain one electron to achieve a stable electron configuration.
- The hydride of bromine is hydrogen bromide (HBr), where bromine has a valency of -1 (HBr).
- However, the higher oxide of bromine, bromine pentoxide (Br2O5), contains bromine with a valency of +5.
- Therefore, bromine does not exhibit identical valency in its hydride and higher oxide.

Ge (Germanium):
- Germanium belongs to group 14, also known as the carbon group.
- The valency of germanium can vary, but it most commonly exhibits a valency of +4 or -4.
- The hydride of germanium is germane (GeH4), where germanium has a valency of +4.
- The higher oxide of germanium, germanium dioxide (GeO2), contains germanium with a valency of +4 as well.
- Therefore, germanium exhibits identical valency (+4) in both its hydride and higher oxide.

As (Arsenic):
- Arsenic belongs to group 15, also known as the nitrogen group.
- The valency of arsenic can vary, but it commonly exhibits a valency of -3 or +3.
- The hydride of arsenic is arsine (AsH3), where arsenic has a valency of -3.
- The higher oxide of arsenic, arsenic pentoxide (As2O5), contains arsenic with a valency of +5.
- Therefore, arsenic does not exhibit identical valency in its hydride and higher oxide.

Se (Selenium):
- Selenium belongs to group 16, also known as the chalcogens.
- The valency of selenium can vary, but it most commonly exhibits a valency of -2 or +6.
- The hydride of selenium is hydrogen selenide (H2Se), where selenium has a valency of -2.
- The higher oxide of selenium, selenium dioxide (SeO2), contains selenium with a valency of +4.
- Therefore, selenium does not exhibit identical valency in its hydride and higher oxide.

Conclusion:
- Out of the given 4th period elements, only Germanium (Ge) exhibits identical valency in its hydride (GeH4) and higher oxide (GeO2).
- Bromine (Br), Arsenic (As), and Selenium (Se) do not exhibit identical valency in their respective hydrides and higher oxides.

(c)