Rishi: Unknown from provided excerpt (hymn-level attribution not supplied here)
Devata: Agni (Hotar, Pāvakaśociṣ)
Chandas: Jagatī or Triṣṭubh (uncertain from the excerpt alone; requires full metrical count by pāda)
Samhita Patha (Devanagari)आग्निं न स्ववृक्तिभिर्होतारं त्वा वृणीमहे । यज्ञाय स्तीर्णबर्हिषे वि वो मदे शीरं पावकशोचिषं विवक्षसे ॥
Recitation with translationRig Veda 10.21.1
Transliterationā́gniṃ na svavṛ́ktibhir hótāraṃ tvā vṛṇīmahe | yajñā́ya stīrṇábarhiṣe ví vo made śīráṃ pāvakáśociṣaṃ vívakṣase ||
Translationわれら自ら織りなす働きによって、アグニよ、汝をホータル(祭官)として選び取る。敷きひろげたバルヒス(祭草座)を備える祭儀のために。われらの歓喜のうちに、汝は顕れ出でんと欲す――強き者、光焔もて浄める輝ける者として。
Word by Wordअग्निम्Agni (as object of choice/praise) स्ववृक्तिभिःwith our choices/acts of choosing (i.e., with our own selections/means) होतारम्the Hotṛ-priest; the invoker स्तीर्णबर्हिषेfor (him/it) whose sacrificial grass is strewn विapart, forth, widely (intensifier) मदेin (your) exhilaration/rapture शीरेम्refreshing drink/sap (milk-like draught) पावकशोचिषम्having purifying flame/radiance विवक्षसेyou wish to speak/utter 
