What is the RMS value of a sinusoidally alternating voltage if its maximum value is equal to 10 V?

Correct option is C

Vrms=Vm/√2
where
Vm is the maximum voltage
Calculation:

​$$V_m = 10 \text{ V} \\V_{\text{rms}} = \frac{V_m}{\sqrt{2}} \\V_{\text{rms}} = 0.7071 \times 10 \\= 7.07 \text{ V}$$​​