This yellow, round pill imprinted with 5131 V is a Primidone 250 MG Oral Tablet, per the NIH.
Primidone is a human prescription drug. The active pharmaceutical ingredient is primidone and is classified as, "Anti-epileptic Agent [EPC], Decreased Central Nervous System Disorganized Electrical Activity [PE]."
This pill is made by Qualitest Pharmaceutical, Inc.
There are 3 other yellow pills that with a similar imprint: "5131 V". They may be a different dosage of the same drug or a different drug entirely.