You are a helpful assistant. When the user asks a question, your response must include two parts: first, the reasoning process enclosed in <think>...</think> tags, then the final answer enclosed in <answer>...</answer> tags.Please provide a clear, concise response within <answer> </answer> tags that directly addresses the question.
system
<image>To spectrophotometrically determine the mass percent of cobalt in an ore containing cobalt and some inert materials, solutions with known [$Co^{2+}$] are prepared and the absorbance of each of the solutions is measured at the wavelength of optimum absorbance. The data are used to create a calibration plot, shown below. <image 1> A 0.630 g sample of the ore is completely dissolved in concentrated $HNO_3$(aq). The mixture is diluted with water to a final volume of 50.00 mL. Assume that all the cobalt in the ore sample is converted to $Co^{2+}$(aq). Calculate the number of moles of $Co^{2+}$(aq) in the 50.00 mL solution. Only write the result number, in the unit of 10^-4 mol.

Please answer the question using a single word or phrase in the format of Answer: <answer>. You FIRST think about the reasoning process as an internal monologue and then provide the final answer. The reasoning process MUST BE enclosed within <think> </think> tags. Please answer the final answer within the <answer> </answer> tags.
user
6.5
To spectrophotometrically determine the mass percent of cobalt in an ore containing cobalt and some inert materials, solutions with known [$Co^{2+}$] are prepared and the absorbance of each of the solutions is measured at the wavelength of optimum absorbance. The data are used to create a calibration plot, shown below. <image 1> A 0.630 g sample of the ore is completely dissolved in concentrated $HNO_3$(aq). The mixture is diluted with water to a final volume of 50.00 mL. Assume that all the cobalt in the ore sample is converted to $Co^{2+}$(aq). Calculate the number of moles of $Co^{2+}$(aq) in the 50.00 mL solution. Only write the result number, in the unit of 10^-4 mol.

Please answer the question using a single word or phrase in the format of Answer: <answer>. You FIRST think about the reasoning process as an internal monologue and then provide the final answer. The reasoning process MUST BE enclosed within <think> </think> tags. Please answer the final answer within the <answer> </answer> tags.
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