Question

if the resistance 1k is open circuited state the effect on voltage across diac

Answer 1

there vont be voltage in open circuit

Answer 2

The V=IR is calculate across any resistor for causing the voltage but it is the potential difference with potential difference as well as some voltage source is current through that resistor.

However, this circuit is open but a voltage source connected for voltage as well as no current will flow up a current should close the circuit.