Some laboratories use the following method to determine the content of substance $\mathbf{A}$ in a certain plant. The structure of $\mathbf{A}$ is shown below:

<MultiModal>![C[C@@H]1CC[C@@]2(C)[C@@H](C)C(=O)O[C@H]3[C@]42[C@@H]1CC[C@@](C)(O3)OO4](/media/uploads/86dffd7f-d364-4899-bfc4-60379211aedd.png)</MultiModal>

Precisely weigh 0.2885 g of potassium dichromate dried at 130°C for two hours, dissolve it in water, and dilute to 100 mL. Transfer 20.00 mL, add 1 g of potassium iodide and 5 mL of 1+5 sulfuric acid, and let it stand in the dark for 5 min. Using starch as the indicator, titrate with sodium thiosulfate solution until the endpoint is reached, consuming 26.24 mL. Then weigh 24.9034 g of the dried plant powder into a dry 250 mL round-bottom flask, add 200 mL of n-pentane, install a Soxhlet extractor, and reflux for 2 h. Filter under suction, dilute with n-pentane to 250 mL. Transfer 25.00 mL of the n-pentane solution, evaporate the n-pentane on a water bath, add 10 mL of anhydrous ethanol, 1 mL of glacial acetic acid, 20 mL of 5% potassium iodide, and 5 mL of 1+1 hydrochloric acid, heat on a water bath at 70°C for 30 minutes, and titrate with sodium thiosulfate using starch as the indicator until the endpoint is reached, consuming 11.73 mL of the standard sodium thiosulfate titration solution.

Among the following statements, at least one is correct (for statements involving calculations, deviations within 1% are considered correct):
1. There are 8 chiral carbon atoms in the structure of $\mathbf{A}$.
2. In the structure of $\mathbf{A}$, there is a carbon atom shared by three six-membered rings, and its stereochemical configuration is R.
3. When extracting $\mathbf{A}$ using a Soxhlet extractor, n-pentane can be replaced with n-hexane.
4. The concentration of the sodium thiosulfate solution is 0.04585 mol/L.
5. The content of $\mathbf{A}$ is 3.000%.

Among these statements, let the number of incorrect statements be a, and the smallest number among the correct statements be b. Then a and b are respectively
有实验室用如下方法测定某植物中某物质$\mathbf{A}$的含量。$\mathbf{A}$的结构如下图所示：

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准确称取在130° C干燥两小时的重铬酸钾0.2885 g，溶于水稀释至100 mL。移取20.00 mL，加1 g碘化钾和5 mL1+5 硫酸，于暗处放置5 min。以淀粉做指示剂，用硫代硫酸钠溶液滴定至终点,消耗26.24 mL。然后称取24.9034 g干燥的该植物粉末于一个干燥的250 mL圆
底烧瓶中，加200 mL正戊烷，安装索氏提取器回流提取2 h。抽滤，用正戊烷稀释至250
 mL。移取25.00 mL正戊烷溶液，在水浴上蒸发除去正戊烷，加入10 mL无水乙醇，1 mL
冰乙酸，20 mL 5%碘化钾，和5 mL1+1盐酸，水浴70 °C加热30 分钟，以淀粉为指示剂用
硫代硫酸钠滴定至终点,消耗硫代硫酸钠标准滴定溶液11.73 mL。

有下列至少一个正确的说法：（涉及到计算的说法，计算误差在1%之内均视为正确）
1. $\mathbf{A}$结构中有8个手性碳原子。
2. $\mathbf{A}$结构中，有一个被三个六元环共用的碳原子，其立体化学构型为R。
3. 利用索氏提取器提取$\mathbf{A}$时，正戊烷可以更换为正己烷。
4. 硫代硫酸钠溶液的浓度为0.04585 mol/L。
5. $\mathbf{A}$的含量为3.000 %。

以上说法中，设错误的说法个数为a，正确的说法中的最小序号为b，则a,b分别为
1, 1
1, 2
1, 3
1, 4
1, 5
2, 1
2, 2
2, 3
2, 4
2, 5
3, 1
3, 2
3, 3
3, 4
3, 5
4, 1
4, 2
4, 3
4, 4
4, 5
1，1
1，2
1，3
1，4
1，5
2，1
2，2
2，3
2，4
2，5
3，1
3，2
3，3
3，4
3，5
4，1
4，2
4，3
4，4
4，5
According to the structure, $\mathbf{A}$ actually has 7 chiral carbon atoms; Statement 1 is incorrect.  

<Checkpoint>[$\mathbf{A}$ actually has 7 chiral carbon atoms](1)</Checkpoint>  

The carbon atom shared by three six-membered rings (one of which is a peroxide six-membered ring, relatively concealed) is the central carbon atom of the structure, with an R stereochemical configuration. Therefore, Statement 2 is correct.  

<Checkpoint>[The carbon atom shared by three six-membered rings is the central carbon atom of the structure, with an R stereochemical configuration](1)</Checkpoint>  

$\mathbf{A}$ contains a bridged ring structure formed by a peroxide bond, which is thermally unstable and prone to decomposition. Thus, n-hexane with too high a boiling point cannot be used as the extraction solvent, making Statement 3 incorrect.  

<Checkpoint>[$\mathbf{A}$ is thermally unstable and prone to decomposition, so n-hexane with too high a boiling point cannot be used as the extraction solvent](1)</Checkpoint>  

The analysis process of $\mathbf{A}$ consists of two steps. First, the sodium thiosulfate solution is standardized using potassium dichromate. According to the stoichiometric relationship, 1 mol $\mathrm{Cr_2O_7^{2-}}$ produces 3 mol $\mathrm{I_2}$, and 1 mol $\mathrm{I_2}$ consumes 2 mol $\mathrm{S_2O_3^{2-}}$. Therefore, n($\mathrm{Cr_2O_7^{2-}}$) : n($\mathrm{I_2}$) = 1 : 6. Substituting the data yields a sodium thiosulfate solution concentration of 0.04485 mol/L, which differs from the 0.04585 mol/L in Statement 4 by more than 1%. Hence, Statement 4 is incorrect.  

<Checkpoint>[The sodium thiosulfate solution concentration is 0.04485 mol/L](1)</Checkpoint>  

The peroxide bond in $\mathbf{A}$ can undergo a redox reaction with potassium iodide, and the generated iodine is back-titrated with sodium thiosulfate solution. The stoichiometric relationship is 1 mol $\mathbf{A}$ ~ 1 mol $\mathrm{I_2}$ ~ 2 mol $\mathrm{S_2O_3^{2-}}$. Substituting the specific data gives a total mass of $\mathbf{A}$ in the sample as 0.7425 g, with a mass percentage of 2.982%, differing from the 3.000% in Statement 5 by less than 1%. Thus, Statement 5 is correct.  

<Checkpoint>[The total mass of $\mathbf{A}$ in the sample is 0.7425 g, with a mass percentage of 2.982%](2)</Checkpoint>  

Therefore, there are 3 incorrect statements in total, and the correct statements are Statements 2 and 5, making Option L correct.  

In fact, $\mathbf{A}$ is artemisinin.
根据结构，$\mathbf{A}$实际上有7个手性碳原子；说法1错误

<Checkpoint>[$\mathbf{A}$实际上有7个手性碳原子](1)</Checkpoint>

被三个六元环（有一个六元环是过氧六元环，比较隐蔽）共用的碳原子即为结构最中心的碳原子，其立体化学构型为R，故说法2正确。

<Checkpoint>[被三个六元环共用的碳原子即为结构最中心的碳原子，其立体化学构型为R](1)</Checkpoint>

$\mathbf{A}$含有由过氧键构成的的桥环结构，对热不稳定，容易分解，从而不能使用沸点太高的正己烷当作提取溶剂，说法3错误。

<Checkpoint>[$\mathbf{A}$对热不稳定，容易分解，从而不能使用沸点太高的正己烷当作提取溶剂](1)</Checkpoint>

$\mathbf{A}$的分析过程分两步，首先是硫代硫酸钠溶液利用重铬酸钾的标定，根据化学计量关系，1 mol $\mathrm{Cr_2O_7^{2-}}$ 产生 3 mol $\mathrm{I_2}$，而 1 mol $\mathrm{I_2}$ 消耗 2 mol $\mathrm{S_2O_3^{2-}}$。因此，n($\mathrm{Cr_2O_7^{2-}}$) : n($\mathrm{I_2}$) = 1 : 6，带入数据可得硫代硫酸钠溶液浓度为0.04485 mol/L，与说法4的0.04585 mol/L差距超过1%，故说法4错误。

<Checkpoint>[硫代硫酸钠溶液浓度为0.04485 mol/L](1)</Checkpoint>

$\mathbf{A}$的过氧键可与碘化钾发生氧化还原反应，生成的碘单质被硫代硫酸钠溶液返滴定。其反应计量关系为1 mol $\mathbf{A}$ ~ 1 mol $\mathrm{I_2}$ ~ 2 mol $\mathrm{S_2O_3^{2-}}$，带入具体数据可得样品中$\mathbf{A}$总质量为0.7425 g，质量百分比为2.982 %，与说法5的3.000 %差距小于1%，说法5正确。

<Checkpoint>[样品中$\mathbf{A}$总质量为0.7425 g，质量百分比为2.982 %](2)</Checkpoint>

因此，错误的说法共有3种，正确说法有说法2，5，故L选项正确。

实际上，$\mathbf{A}$就是青蒿素。