Potentials of certain points in the circuit are maintained as marked. What is reading of voltmeter, if the ammeter reads zero ?

From figure, VA−(−5)=5V⇒VA=0 As reading of ammeter is zero, V=0 across 2Ω in series with ammeter. ∴VB=0 Apply loop law to the loop ABCDVA, P.D. across voltmeter =10V∵VAB=0