Question

SAT化学的三个问题！急！！！多谢各位

1. To the correct number of significant figures, what is the mass of 2.5 moles deuterium gas(isotope mass=2.014 amu)?
A. 5.035g
B. 5.0g
这个有效数字究竟是按2位算还是4位算？答案是A，但是根据乘法有效数字的计算法则，不是应该是2位吗？

2. A nearly equal volume of NaOH solution and acid are have been added.
判断正误？答案说是错误的。我的疑惑在于：首先我没看懂这句话的意思，其次这句话怎么判断？

Dropper pipette: Used to add small amounts of liquid to a solution, but only when a precise volume is not needed {because the drops themselves should be consistent only for one particular dropper (i.e. adding an indicator, comparing the amount of drops of strong acid or base needed for a pH change in different solutions)}
{}部分什么意思？
回答的好再加分！
根据乘法有效数字的计算法则，不是取有效数字位数少的吗？

Answer 1

1 你拿2.014和2.5乘，根据乘法有效数字的计算法则，不应该得出4位有效数字吗？

2i.e. adding an indicator, comparing the amount of drops of strong acid or base needed for a pH change in different solutions
是说要你用指示剂，因为 pipette本身不精确。加强精确度。

判断正误。。不懂。