Statement I: In 3d series Cu, Cr exhibit +1 oxidation state also

Statement II: In these two, the outer most (ns) orbital is completely filled.

Statement I is true but statement II is false

The correct answer is option 3. Statement I is true but statement II is false.

Let us break down the statements and provide an explanation:

Statement I: In the 3d series, Cu and Cr exhibit +1 oxidation state also.

Copper commonly exhibits +1 and +2 oxidation states. In the +1 oxidation state, the electron configuration is \([Ar] 3d^{10}\). So, this part of the statement is true for copper.

Chromium typically exhibits +2, +3, and +6 oxidation states. While chromium can, in rare cases, exhibit a +1 oxidation state, it is not a common or stable oxidation state for chromium.

Statement I is  correct because Cu does exhibit a +1 oxidation state, but Cr does not commonly exhibit a +1 oxidation state, but it can show the +1 oxidation state.

Statement II: In these two, the outermost (ns) orbital is completely filled.

Ground state electron configuration: \([Ar] 3d^{10} 4s^1\).

In the +1 oxidation state \((Cu^+)\), the configuration is \([Ar] 3d^{10}\). The \(4s\) electron is lost, and the \(4s\) orbital is not filled.

Ground state electron configuration: \([Ar] 3d^{5} 4s^1\).  In the +1 oxidation state \((Cr^+)\), the configuration would be \([Ar] 3d^5\). The \(4s\) electron is lost, and the \(4s\) orbital is not filled.

Statement II is false because the outermost \((ns)\) orbital is not completely filled in either \(Cu\) or \(Cr\) in their ground states or +1 oxidation states.

Therefore, the correct option is 3. Statement I is true but Statement II is false.