By using Arrhenius equation,
logK2K1=Ea2.303R[1T1−1T2]Where,K2 is rate constant at T2 (300K)K1 is rate constant at T1 (200K)R is universal gas constant = 8.314 J K−1 mol−1Substituting the values, we getlog1.0×10−3s−1K1=11.488×10002.303×8.314[1200−1300]log10−3K1=600×3−2600log10−3K1=1⇒10=10−3K1⇒K1=10−4 s−1So, x×10−5=10−4⇒x=10