Second-declension noun.
What declension is Rex?
SINGULARPLURALNOM.rexregesGEN.regisregumDAT.regiregibusACC.regemreges
What declension is pulchra?
pulcher (feminine pulchra, neuter pulchrum, comparative pulchrior, superlative pulcherrimus, adverb pulchrē); first/second-declension adjective (nominative masculine singular in -er)