The principal ores of iron are :
Siderite, Haematite, Magnetite, Limonite.
Consider an A.P. $a_1,a_2,\ldots,a_n$; $a_1>0$. If $a_2-a_1=-\dfrac{3}{4}$, $a_n=\dfrac{1}{4}a_1$, and \[ \sum_{i=1}^{n} a_i=\frac{525}{2}, \] then $\sum_{i=1}^{17} a_i$ is equal to

SN1 reaction mechanism takes place by following three steps –
The SN2 reaction mechanism involves the nucleophilic substitution reaction of the leaving group (which generally consists of halide groups or other electron-withdrawing groups) with a nucleophile in a given organic compound.
The mechanism of an electrophilic aromatic substitution reaction contains three main components which are:
The electrophilic substitution reaction mechanism is composed of three steps, which will be discussed more below.