Which d-block metal pair does not exhibit variable oxidation state?

Transition elements (d-block)

Read the following passage and answer the questions given:

The d-block occupies the large middle section of the periodic table flanked between s- and p-blocks in the modern periodic table. These elements have a general electronic configuration (n-1)d^1-10 ns² (except Pd). These elements possess a partially filled penultimate d-subshell in their ground state. Most of the transition element compounds are colored in solid or in solution state which arise due to excitation of electrons from lower energy d-orbitals to higher energy d-orbitals. The transition metal ions which have completely filled d-orbitals are colorless due to lack of excitation within d-orbitals. Most of the transition metals and their compounds exhibit paramagnetic behavior (attracted by a magnetic field) which is attributed to an incomplete d-subshell and the presence of unpaired electrons. An element or ion having no unpaired electron shows diamagnetic behavior (repelled by a magnetic field). The magnetic moment of transition elements arises due to spin and orbital motion in ions or molecules. The magnetic moment is determined by the number of unpaired electrons (n) and is calculated by using the spin-only formula μ= [n (n+2)]^1/2 Bohr magneton (BM). The magnetic moment increases with the increasing number of unpaired electrons. Thus, the observed magnetic moment gives a useful indication about the number of unpaired electrons present in the transition metal or its ions. Transition elements exhibit certain important characteristic properties such as variable oxidation state, complex formation, colored ion formation, catalytic activity and metallic properties like high tensile strength, ductility, malleability etc. Transition metals are hard and have high melting points (with exceptions of Zn, Cd, Hg).